diff --git a/actions/apiaccountratelimitstatus.php b/actions/apiaccountratelimitstatus.php
index 8d7f89eadc..8490e2965c 100644
--- a/actions/apiaccountratelimitstatus.php
+++ b/actions/apiaccountratelimitstatus.php
@@ -66,6 +66,7 @@ class ApiAccountRateLimitStatusAction extends ApiBareAuthAction
 
         if (!in_array($this->format, array('xml', 'json'))) {
             $this->clientError(
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apiaccountupdatedeliverydevice.php b/actions/apiaccountupdatedeliverydevice.php
index a36806b216..57e4fbfa00 100644
--- a/actions/apiaccountupdatedeliverydevice.php
+++ b/actions/apiaccountupdatedeliverydevice.php
@@ -88,7 +88,7 @@ class ApiAccountUpdateDeliveryDeviceAction extends ApiAuthAction
 
         if (!in_array($this->format, array('xml', 'json'))) {
             $this->clientError(
-                // TRANS: Client error displayed handling a non-existing API method.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apiaccountupdateprofile.php b/actions/apiaccountupdateprofile.php
index d0b9abe9b7..a572131f18 100644
--- a/actions/apiaccountupdateprofile.php
+++ b/actions/apiaccountupdateprofile.php
@@ -90,7 +90,7 @@ class ApiAccountUpdateProfileAction extends ApiAuthAction
 
         if (!in_array($this->format, array('xml', 'json'))) {
             $this->clientError(
-                // TRANS: Client error displayed when trying to handle an unknown API method.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apiaccountupdateprofilebackgroundimage.php b/actions/apiaccountupdateprofilebackgroundimage.php
index f26c30198d..36eaa6c411 100644
--- a/actions/apiaccountupdateprofilebackgroundimage.php
+++ b/actions/apiaccountupdateprofilebackgroundimage.php
@@ -88,7 +88,7 @@ class ApiAccountUpdateProfileBackgroundImageAction extends ApiAuthAction
 
         if (!in_array($this->format, array('xml', 'json'))) {
             $this->clientError(
-                // TRANS: Client error displayed when trying to handle an unknown API method.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apiaccountupdateprofilecolors.php b/actions/apiaccountupdateprofilecolors.php
index 4c102c4090..621b05b0d9 100644
--- a/actions/apiaccountupdateprofilecolors.php
+++ b/actions/apiaccountupdateprofilecolors.php
@@ -111,7 +111,7 @@ class ApiAccountUpdateProfileColorsAction extends ApiAuthAction
 
         if (!in_array($this->format, array('xml', 'json'))) {
             $this->clientError(
-                // TRANS: Client error displayed trying to execute an unknown API method updating profile colours.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apiaccountverifycredentials.php b/actions/apiaccountverifycredentials.php
index 26d4e2fc5c..359939b0cc 100644
--- a/actions/apiaccountverifycredentials.php
+++ b/actions/apiaccountverifycredentials.php
@@ -64,7 +64,7 @@ class ApiAccountVerifyCredentialsAction extends ApiAuthAction
         parent::handle($args);
 
         if (!in_array($this->format, array('xml', 'json'))) {
-            // TRANS: Client error displayed trying to execute an unknown API method verifying user credentials.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), $code = 404);
             return;
         }
diff --git a/actions/apidirectmessage.php b/actions/apidirectmessage.php
index e072e27b83..584decc747 100644
--- a/actions/apidirectmessage.php
+++ b/actions/apidirectmessage.php
@@ -153,7 +153,7 @@ class ApiDirectMessageAction extends ApiAuthAction
             $this->showJsonDirectMessages();
             break;
         default:
-            // TRANS: Client error given when an API method was not found (404).
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), $code = 404);
             break;
         }
diff --git a/actions/apifavoritecreate.php b/actions/apifavoritecreate.php
index b2f6266ebf..b890d4af69 100644
--- a/actions/apifavoritecreate.php
+++ b/actions/apifavoritecreate.php
@@ -94,7 +94,7 @@ class ApiFavoriteCreateAction extends ApiAuthAction
 
         if (!in_array($this->format, array('xml', 'json'))) {
             $this->clientError(
-                // TRANS: Client error displayed when trying to handle an unknown API method.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apifavoritedestroy.php b/actions/apifavoritedestroy.php
index f86c985dc0..db121ac882 100644
--- a/actions/apifavoritedestroy.php
+++ b/actions/apifavoritedestroy.php
@@ -94,7 +94,7 @@ class ApiFavoriteDestroyAction extends ApiAuthAction
 
         if (!in_array($this->format, array('xml', 'json'))) {
             $this->clientError(
-                // TRANS: Client error displayed when trying to handle an unknown API method.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apifriendshipscreate.php b/actions/apifriendshipscreate.php
index 89557f8392..9932809818 100644
--- a/actions/apifriendshipscreate.php
+++ b/actions/apifriendshipscreate.php
@@ -95,7 +95,7 @@ class ApiFriendshipsCreateAction extends ApiAuthAction
 
         if (!in_array($this->format, array('xml', 'json'))) {
             $this->clientError(
-                // TRANS: Client error displayed when trying to handle an unknown API method.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apifriendshipsdestroy.php b/actions/apifriendshipsdestroy.php
index a5dff08bab..1534aa799f 100644
--- a/actions/apifriendshipsdestroy.php
+++ b/actions/apifriendshipsdestroy.php
@@ -95,7 +95,7 @@ class ApiFriendshipsDestroyAction extends ApiAuthAction
 
         if (!in_array($this->format, array('xml', 'json'))) {
             $this->clientError(
-                // TRANS: Client error displayed when trying to handle an unknown API method.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apifriendshipsshow.php b/actions/apifriendshipsshow.php
index 6b069c4fcf..1eaca49f0e 100644
--- a/actions/apifriendshipsshow.php
+++ b/actions/apifriendshipsshow.php
@@ -120,7 +120,7 @@ class ApiFriendshipsShowAction extends ApiBareAuthAction
         parent::handle($args);
 
         if (!in_array($this->format, array('xml', 'json'))) {
-            // TRANS: Client error displayed trying to execute an unknown API method showing friendship.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), 404);
             return;
         }
diff --git a/actions/apigroupcreate.php b/actions/apigroupcreate.php
index d01504bc80..8615bcff7e 100644
--- a/actions/apigroupcreate.php
+++ b/actions/apigroupcreate.php
@@ -134,7 +134,7 @@ class ApiGroupCreateAction extends ApiAuthAction
             break;
         default:
             $this->clientError(
-                // TRANS: Client error given when an API method was not found (404).
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apigroupismember.php b/actions/apigroupismember.php
index 8d31c65ddb..13ed9e1fbf 100644
--- a/actions/apigroupismember.php
+++ b/actions/apigroupismember.php
@@ -111,7 +111,7 @@ class ApiGroupIsMemberAction extends ApiBareAuthAction
             break;
         default:
             $this->clientError(
-                // TRANS: Client error displayed trying to execute an unknown API method showing group membership.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 400,
                 $this->format
diff --git a/actions/apigroupjoin.php b/actions/apigroupjoin.php
index 7124a4b0f0..6f3df0d8cd 100644
--- a/actions/apigroupjoin.php
+++ b/actions/apigroupjoin.php
@@ -144,7 +144,7 @@ class ApiGroupJoinAction extends ApiAuthAction
             break;
         default:
             $this->clientError(
-                // TRANS: Client error displayed trying to execute an unknown API method joining a group.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apigroupleave.php b/actions/apigroupleave.php
index 35a4e04d78..9d2825b00e 100644
--- a/actions/apigroupleave.php
+++ b/actions/apigroupleave.php
@@ -134,7 +134,7 @@ class ApiGroupLeaveAction extends ApiAuthAction
             break;
         default:
             $this->clientError(
-                // TRANS: Client error displayed trying to execute an unknown API method leaving a group.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apigrouplist.php b/actions/apigrouplist.php
index f80fbce932..c7518ca129 100644
--- a/actions/apigrouplist.php
+++ b/actions/apigrouplist.php
@@ -67,6 +67,7 @@ class ApiGroupListAction extends ApiBareAuthAction
         $this->user   = $this->getTargetUser(null);
 
         if (empty($this->user)) {
+            // TRANS: Client error displayed when user not found for an action.
             $this->clientError(_('No such user.'), 404, $this->format);
             return false;
         }
@@ -130,7 +131,7 @@ class ApiGroupListAction extends ApiBareAuthAction
             break;
         default:
             $this->clientError(
-                // TRANS: Client error displayed trying to execute an unknown API method checking group membership.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apigrouplistall.php b/actions/apigrouplistall.php
index d05baa0992..65ff9ae59a 100644
--- a/actions/apigrouplistall.php
+++ b/actions/apigrouplistall.php
@@ -116,7 +116,7 @@ class ApiGroupListAllAction extends ApiPrivateAuthAction
             break;
         default:
             $this->clientError(
-                // TRANS: Client error displayed trying to execute an unknown API method listing the latest 20 groups.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apigroupmembership.php b/actions/apigroupmembership.php
index 939d22d757..7ad8fb767e 100644
--- a/actions/apigroupmembership.php
+++ b/actions/apigroupmembership.php
@@ -101,7 +101,7 @@ class ApiGroupMembershipAction extends ApiPrivateAuthAction
             break;
         default:
             $this->clientError(
-                // TRANS: Client error displayed trying to execute an unknown API method showing group membership.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apigroupprofileupdate.php b/actions/apigroupprofileupdate.php
index 9a629a47d7..379e01a428 100644
--- a/actions/apigroupprofileupdate.php
+++ b/actions/apigroupprofileupdate.php
@@ -85,6 +85,7 @@ class ApiGroupProfileUpdateAction extends ApiAuthAction
 
         if ($_SERVER['REQUEST_METHOD'] != 'POST') {
             $this->clientError(
+                // TRANS: Client error message. POST is a HTTP command. It should not be translated.
                 _('This method requires a POST.'),
                 400, $this->format
             );
@@ -93,7 +94,7 @@ class ApiGroupProfileUpdateAction extends ApiAuthAction
 
         if (!in_array($this->format, array('xml', 'json'))) {
             $this->clientError(
-                // TRANS: Client error displayed when using an unsupported API format.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
@@ -211,7 +212,7 @@ class ApiGroupProfileUpdateAction extends ApiAuthAction
             $this->showSingleJsonGroup($this->group);
             break;
         default:
-            // TRANS: Client error displayed when using an unsupported API format.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), 404, $this->format);
             break;
         }
diff --git a/actions/apigroupshow.php b/actions/apigroupshow.php
index 471aa141f9..a7385ffaaf 100644
--- a/actions/apigroupshow.php
+++ b/actions/apigroupshow.php
@@ -110,7 +110,7 @@ class ApiGroupShowAction extends ApiPrivateAuthAction
             $this->showSingleJsonGroup($this->group);
             break;
         default:
-            // TRANS: Client error displayed trying to execute an unknown API method showing a group.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), 404, $this->format);
             break;
         }
diff --git a/actions/apihelptest.php b/actions/apihelptest.php
index fbe5f12784..1bbbe572bf 100644
--- a/actions/apihelptest.php
+++ b/actions/apihelptest.php
@@ -80,7 +80,7 @@ class ApiHelpTestAction extends ApiPrivateAuthAction
             $this->endDocument('json');
         } else {
             $this->clientError(
-                // TRANS: Client error displayed trying to execute an unknown API method testing API connectivity.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apistatusesdestroy.php b/actions/apistatusesdestroy.php
index d73e574b3c..b4a8870faa 100644
--- a/actions/apistatusesdestroy.php
+++ b/actions/apistatusesdestroy.php
@@ -97,7 +97,7 @@ class ApiStatusesDestroyAction extends ApiAuthAction
 
         if (!in_array($this->format, array('xml', 'json'))) {
             $this->clientError(
-                // TRANS: Client error displayed trying to execute an unknown API method deleting a status.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404
             );
diff --git a/actions/apistatusesretweets.php b/actions/apistatusesretweets.php
index cc7caee19d..7220196836 100644
--- a/actions/apistatusesretweets.php
+++ b/actions/apistatusesretweets.php
@@ -106,7 +106,7 @@ class ApiStatusesRetweetsAction extends ApiAuthAction
             $this->showJsonTimeline($strm);
             break;
         default:
-            // TRANS: Client error displayed when trying to handle an unknown API method.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), $code = 404);
             break;
         }
diff --git a/actions/apistatusesshow.php b/actions/apistatusesshow.php
index de4c4065c1..13cc88c2c7 100644
--- a/actions/apistatusesshow.php
+++ b/actions/apistatusesshow.php
@@ -101,7 +101,7 @@ class ApiStatusesShowAction extends ApiPrivateAuthAction
         parent::handle($args);
 
         if (!in_array($this->format, array('xml', 'json', 'atom'))) {
-            // TRANS: Client error displayed when trying to handle an unknown API method.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), 404);
             return;
         }
diff --git a/actions/apistatusesupdate.php b/actions/apistatusesupdate.php
index 5773bdc2e8..b0f3527160 100644
--- a/actions/apistatusesupdate.php
+++ b/actions/apistatusesupdate.php
@@ -239,8 +239,8 @@ class ApiStatusesUpdateAction extends ApiAuthAction
 
             $this->clientError(
                 sprintf(
-                    // TRANS: Client error displayed when the parameter "status" is missing.
-                    // TRANS: %d is the maximum number of character for a notice.
+                    // TRANS: Client error displayed exceeding the maximum notice length.
+                    // TRANS: %d is the maximum length for a notice.
                     _m('That\'s too long. Maximum notice size is %d character.',
                       'That\'s too long. Maximum notice size is %d characters.',
                       Notice::maxContent()),
diff --git a/actions/apistatusnetconfig.php b/actions/apistatusnetconfig.php
index b34c6cc544..7cd7c5ed6c 100644
--- a/actions/apistatusnetconfig.php
+++ b/actions/apistatusnetconfig.php
@@ -135,7 +135,7 @@ class ApiStatusnetConfigAction extends ApiAction
             break;
         default:
             $this->clientError(
-                // TRANS: Client error displayed when trying to handle an unknown API method.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apistatusnetversion.php b/actions/apistatusnetversion.php
index bc2babc3f2..3a7b150cab 100644
--- a/actions/apistatusnetversion.php
+++ b/actions/apistatusnetversion.php
@@ -87,7 +87,7 @@ class ApiStatusnetVersionAction extends ApiPrivateAuthAction
             break;
         default:
             $this->clientError(
-                // TRANS: Client error displayed when trying to handle an unknown API method.
+                // TRANS: Client error displayed when coming across a non-supported API method.
                 _('API method not found.'),
                 404,
                 $this->format
diff --git a/actions/apisubscriptions.php b/actions/apisubscriptions.php
index fc0a2638b6..84731ac00f 100644
--- a/actions/apisubscriptions.php
+++ b/actions/apisubscriptions.php
@@ -105,7 +105,7 @@ class ApiSubscriptionsAction extends ApiBareAuthAction
         parent::handle($args);
 
         if (!in_array($this->format, array('xml', 'json'))) {
-            // TRANS: Client error displayed when trying to handle an unknown API method.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), $code = 404);
             return;
         }
diff --git a/actions/apitimelinefavorites.php b/actions/apitimelinefavorites.php
index 36fc3089f5..2c962b450a 100644
--- a/actions/apitimelinefavorites.php
+++ b/actions/apitimelinefavorites.php
@@ -178,7 +178,7 @@ class ApiTimelineFavoritesAction extends ApiBareAuthAction
             $this->raw($doc->asString());
             break;
         default:
-            // TRANS: Client error displayed when trying to handle an unknown API method.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), $code = 404);
             break;
         }
diff --git a/actions/apitimelinefriends.php b/actions/apitimelinefriends.php
index 0e356bb18b..00eb4de502 100644
--- a/actions/apitimelinefriends.php
+++ b/actions/apitimelinefriends.php
@@ -204,6 +204,8 @@ class ApiTimelineFriendsAction extends ApiBareAuthAction
         $profile    = $this->user->getProfile();
         $avatar     = $profile->getAvatar(AVATAR_PROFILE_SIZE);
         $sitename   = common_config('site', 'name');
+        // TRANS: Title of API timeline for a user and friends.
+        // TRANS: %s is a username.
         $title      = sprintf(_("%s and friends"), $this->user->nickname);
         $taguribase = TagURI::base();
         $id         = "tag:$taguribase:FriendsTimeline:" . $this->user->id;
@@ -272,7 +274,7 @@ class ApiTimelineFriendsAction extends ApiBareAuthAction
             $this->raw($doc->asString());
             break;
         default:
-            // TRANS: Client error displayed when trying to handle an unknown API method.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), $code = 404);
             break;
         }
diff --git a/actions/apitimelinehome.php b/actions/apitimelinehome.php
index 023c9698a1..96642cbfab 100644
--- a/actions/apitimelinehome.php
+++ b/actions/apitimelinehome.php
@@ -177,7 +177,7 @@ class ApiTimelineHomeAction extends ApiBareAuthAction
             $this->raw($doc->asString());
             break;
         default:
-            // TRANS: Client error displayed when trying to handle an unknown API method.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), $code = 404);
             break;
         }
diff --git a/actions/apitimelinementions.php b/actions/apitimelinementions.php
index 2857bd41ea..ecd2a1a0e6 100644
--- a/actions/apitimelinementions.php
+++ b/actions/apitimelinementions.php
@@ -178,7 +178,7 @@ class ApiTimelineMentionsAction extends ApiBareAuthAction
             $this->raw($doc->asString());
             break;
         default:
-            // TRANS: Client error displayed when trying to handle an unknown API method.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), $code = 404);
             break;
         }
diff --git a/actions/apitimelinepublic.php b/actions/apitimelinepublic.php
index 353973b653..a786aa15cc 100644
--- a/actions/apitimelinepublic.php
+++ b/actions/apitimelinepublic.php
@@ -243,7 +243,7 @@ class ApiTimelinePublicAction extends ApiPrivateAuthAction
             $this->raw($doc->asString());
             break;
         default:
-            // TRANS: Client error displayed when trying to handle an unknown API method.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), $code = 404);
             break;
         }
diff --git a/actions/apitimelineretweetedtome.php b/actions/apitimelineretweetedtome.php
index 628dc40247..ef943f4f88 100644
--- a/actions/apitimelineretweetedtome.php
+++ b/actions/apitimelineretweetedtome.php
@@ -146,7 +146,7 @@ class ApiTimelineRetweetedToMeAction extends ApiAuthAction
             $this->raw($doc->asString());
             break;
         default:
-            // TRANS: Client error displayed when trying to handle an unknown API method.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), $code = 404);
             break;
         }
diff --git a/actions/apitimelineretweetsofme.php b/actions/apitimelineretweetsofme.php
index aec6877f15..d38e730ac6 100644
--- a/actions/apitimelineretweetsofme.php
+++ b/actions/apitimelineretweetsofme.php
@@ -101,6 +101,8 @@ class ApiTimelineRetweetsOfMeAction extends ApiAuthAction
         $profile = $this->auth_user->getProfile();
 
         $subtitle   = sprintf(
+            // TRANS: Subtitle of API time with retweets of me.
+            // TRANS: %1$s is the StatusNet sitename, %2$s is the user nickname, %3$s is the user profile name.
             _('%1$s notices that %2$s / %3$s has repeated.'),
             $sitename, $this->auth_user->nickname, $profile->getBestName()
         );
@@ -143,7 +145,7 @@ class ApiTimelineRetweetsOfMeAction extends ApiAuthAction
             $this->raw($doc->asString());
             break;
         default:
-            // TRANS: Client error displayed when trying to handle an unknown API method.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), 404);
             break;
         }
diff --git a/actions/apitimelinetag.php b/actions/apitimelinetag.php
index 5fa76d0cd0..6c3b135ed9 100644
--- a/actions/apitimelinetag.php
+++ b/actions/apitimelinetag.php
@@ -161,7 +161,7 @@ class ApiTimelineTagAction extends ApiPrivateAuthAction
             $this->raw($doc->asString());
             break;
         default:
-            // TRANS: Client error displayed when trying to handle an unknown API method.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), $code = 404);
             break;
         }
diff --git a/actions/apitimelineuser.php b/actions/apitimelineuser.php
index 3fe73c691c..b0681c191a 100644
--- a/actions/apitimelineuser.php
+++ b/actions/apitimelineuser.php
@@ -213,7 +213,7 @@ class ApiTimelineUserAction extends ApiBareAuthAction
             $this->raw($doc->asString());
             break;
         default:
-            // TRANS: Client error displayed when trying to handle an unknown API method.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), $code = 404);
             break;
         }
diff --git a/actions/apiusershow.php b/actions/apiusershow.php
index fbd4d60598..ab1bfb9c9c 100644
--- a/actions/apiusershow.php
+++ b/actions/apiusershow.php
@@ -96,7 +96,7 @@ class ApiUserShowAction extends ApiPrivateAuthAction
         }
 
         if (!in_array($this->format, array('xml', 'json'))) {
-            // TRANS: Client error displayed when trying to handle an unknown API method.
+            // TRANS: Client error displayed when coming across a non-supported API method.
             $this->clientError(_('API method not found.'), $code = 404);
             return;
         }
diff --git a/actions/newnotice.php b/actions/newnotice.php
index 3b7cabaced..97282e215d 100644
--- a/actions/newnotice.php
+++ b/actions/newnotice.php
@@ -181,6 +181,8 @@ class NewnoticeAction extends Action
 
             if (Notice::contentTooLong($content_shortened)) {
                 $upload->delete();
+                // TRANS: Client error displayed exceeding the maximum notice length.
+                // TRANS: %d is the maximum length for a notice.
                 $this->clientError(sprintf(_m('Maximum notice size is %d character, including attachment URL.',
                                               'Maximum notice size is %d characters, including attachment URL.',
                                               Notice::maxContent()),
diff --git a/actions/register.php b/actions/register.php
index d8f752d2bb..e5f3ef1080 100644
--- a/actions/register.php
+++ b/actions/register.php
@@ -212,6 +212,7 @@ class RegisterAction extends Action
                 // TRANS: Form validation error displayed when trying to register with an invalid nickname.
                 $this->showForm(_('Not a valid nickname.'));
             } else if ($this->emailExists($email)) {
+                // TRANS: Form validation error displayed when trying to register with an already registered e-mail address.
                 $this->showForm(_('Email address already exists.'));
             } else if (!is_null($homepage) && (strlen($homepage) > 0) &&
                        !Validate::uri($homepage,
diff --git a/actions/userrss.php b/actions/userrss.php
index ba9f64f8ac..b60cc5e0c7 100644
--- a/actions/userrss.php
+++ b/actions/userrss.php
@@ -37,6 +37,7 @@ class UserrssAction extends Rss10Action
         $this->tag  = $this->trimmed('tag');
 
         if (!$this->user) {
+            // TRANS: Client error displayed when user not found for an action.
             $this->clientError(_('No such user.'));
             return false;
         } else {
@@ -105,6 +106,7 @@ class UserrssAction extends Rss10Action
         $profile = $user->getProfile();
         if (!$profile) {
             common_log_db_error($user, 'SELECT', __FILE__);
+            // TRANS: Server error displayed in user RSS when user does not have a matching profile.
             $this->serverError(_('User without matching profile.'));
             return null;
         }
diff --git a/actions/userxrd.php b/actions/userxrd.php
index 7691ff155b..1d888064d6 100644
--- a/actions/userxrd.php
+++ b/actions/userxrd.php
@@ -56,6 +56,7 @@ class UserxrdAction extends XrdAction
         }
 
         if (!$this->user) {
+            // TRANS: Client error displayed when user not found for an action.
             $this->clientError(_('No such user.'), 404);
             return false;
         }