diff --git a/lib/mailbox.php b/lib/mailbox.php
index e9e4f78c6b..7c6567c6c1 100644
--- a/lib/mailbox.php
+++ b/lib/mailbox.php
@@ -42,7 +42,6 @@ if (!defined('STATUSNET') && !defined('LACONICA')) {
  * @see      InboxAction
  * @see      OutboxAction
  */
-
 class MailboxAction extends CurrentUserDesignAction
 {
     var $page = null;
@@ -71,12 +70,12 @@ class MailboxAction extends CurrentUserDesignAction
      *
      * @return void
      */
-
     function handle($args)
     {
         parent::handle($args);
 
         if (!$this->user) {
+            // TRANS: Client error displayed when trying to access a mailbox without providing a user.
             $this->clientError(_('No such user.'), 404);
             return;
         }
@@ -84,6 +83,7 @@ class MailboxAction extends CurrentUserDesignAction
         $cur = common_current_user();
 
         if (!$cur || $cur->id != $this->user->id) {
+            // TRANS: Client error displayed when trying to access a mailbox that is not of the logged in user.
             $this->clientError(_('Only the user can read their own mailboxes.'),
                 403);
             return;
@@ -114,8 +114,9 @@ class MailboxAction extends CurrentUserDesignAction
                               $this->trimmed('action'),
                               array('nickname' => $this->user->nickname));
         } else {
-            $this->element('p', 
-                           'guide', 
+            $this->element('p',
+                           'guide',
+                           // TRANS: Message displayed when there are no private messages in the inbox of a user.
                            _('You have no private messages. '.
                              'You can send private message to engage other users in conversation. '.
                              'People can send you messages for your eyes only.'));
@@ -139,7 +140,6 @@ class MailboxAction extends CurrentUserDesignAction
      *
      * @return void
      */
-
     function showPageNotice()
     {
         $instr  = $this->getInstructions();
@@ -157,7 +157,6 @@ class MailboxAction extends CurrentUserDesignAction
      *
      * @return boolean
      */
-
     function isReadOnly($args)
     {
          return true;
diff --git a/lib/mailboxmenu.php b/lib/mailboxmenu.php
index d2d3607dce..49e7dce21a 100644
--- a/lib/mailboxmenu.php
+++ b/lib/mailboxmenu.php
@@ -4,7 +4,7 @@
  * Copyright (C) 2011, StatusNet, Inc.
  *
  * Private mailboxes menu
- * 
+ *
  * PHP version 5
  *
  * This program is free software: you can redistribute it and/or modify
@@ -44,7 +44,6 @@ if (!defined('STATUSNET')) {
  * @license   http://www.fsf.org/licensing/licenses/agpl-3.0.html AGPL 3.0
  * @link      http://status.net/
  */
-
 class MailboxMenu extends Menu
 {
     function show()
@@ -56,15 +55,18 @@ class MailboxMenu extends Menu
 
         $this->item('inbox',
                     array('nickname' => $nickname),
-                    _('Inbox'),
-                    _('Your incoming messages'));
+                    // TRANS: Menu item in mailbox menu. Leads to incoming private messages.
+                    _m('MENU','Inbox'),
+                    // TRANS: Menu item title in mailbox menu. Leads to incoming private messages.
+                    _('Your incoming messages.'));
 
         $this->item('outbox',
                     array('nickname' => $nickname),
-                    _('Outbox'),
-                    _('Your sent messages'));
+                    // TRANS: Menu item in mailbox menu. Leads to outgoing private messages.
+                    _m('MENU','Outbox'),
+                    // TRANS: Menu item title in mailbox menu. Leads to outgoing private messages.
+                    _('Your sent messages.'));
 
         $this->out->elementEnd('ul');
     }
-
 }
diff --git a/lib/mailhandler.php b/lib/mailhandler.php
index bbeb69a8f9..65c5622de3 100644
--- a/lib/mailhandler.php
+++ b/lib/mailhandler.php
@@ -21,7 +21,7 @@ require_once(INSTALLDIR . '/lib/mail.php');
 require_once(INSTALLDIR . '/lib/mediafile.php');
 require_once('Mail/mimeDecode.php');
 
-// FIXME: we use both Mail_mimeDecode and mailparse
+// @todo FIXME: we use both Mail_mimeDecode and mailparse
 // Need to move everything to mailparse
 
 class MailHandler
@@ -34,19 +34,23 @@ class MailHandler
     {
         list($from, $to, $msg, $attachments) = $this->parse_message($rawmessage);
         if (!$from || !$to || !$msg) {
+            // TRANS: Error message in incoming mail handler used when an incoming e-mail cannot be processed.
             $this->error(null, _('Could not parse message.'));
         }
         common_log(LOG_INFO, "Mail from $from to $to with ".count($attachments) .' attachment(s): ' .substr($msg, 0, 20));
         $user = $this->user_from_header($from);
         if (!$user) {
+            // TRANS: Error message in incoming mail handler used when an incoming e-mail is not from a registered user.
             $this->error($from, _('Not a registered user.'));
             return false;
         }
         if (!$this->user_match_to($user, $to)) {
+            // TRANS: Error message in incoming mail handler used when an incoming e-mail is not from a user's incoming e-mail address.
             $this->error($from, _('Sorry, that is not your incoming email address.'));
             return false;
         }
         if (!$user->emailpost) {
+            // TRANS: Error message in incoming mail handler used when no incoming e-mail is allowed.
             $this->error($from, _('Sorry, no incoming email allowed.'));
             return false;
         }
@@ -57,7 +61,8 @@ class MailHandler
         $msg = $this->cleanup_msg($msg);
         $msg = $user->shortenLinks($msg);
         if (Notice::contentTooLong($msg)) {
-            $this->error($from, sprintf(_('That\'s too long. Maximum notice size is %d character.',
+            // TRANS: Error message in incoming mail handler used when an incoming e-mail contains too many characters.
+            $this->error($from, sprintf(_m('That\'s too long. Maximum notice size is %d character.',
                                           'That\'s too long. Maximum notice size is %d characters.',
                                           Notice::maxContent()),
                                         Notice::maxContent()));
@@ -66,7 +71,6 @@ class MailHandler
         $mediafiles = array();
 
         foreach($attachments as $attachment){
-
             $mf = null;
 
             try {
@@ -137,9 +141,9 @@ class MailHandler
 
     function respond($from, $to, $response)
     {
-
         $headers['From'] = $to;
         $headers['To'] = $from;
+        // TRANS: E-mail subject for reply to an e-mail command.
         $headers['Subject'] = _('Command complete');
 
         return mail_send(array($from), $headers, $response);
@@ -226,7 +230,9 @@ class MailHandler
 
     function unsupported_type($type)
     {
-        $this->error(null, sprintf(_('Unsupported message type: %s'), $type));
+        // TRANS: Error message in incoming mail handler used when an incoming e-mail is of an unsupported type.
+        // TRANS: %s is the unsupported type.
+        $this->error(null, sprintf(_('Unsupported message type: %s.'), $type));
     }
 
     function cleanup_msg($msg)
diff --git a/lib/messageform.php b/lib/messageform.php
index 733e83cd15..bd46d7389d 100644
--- a/lib/messageform.php
+++ b/lib/messageform.php
@@ -46,19 +46,16 @@ require_once INSTALLDIR.'/lib/form.php';
  *
  * @see      HTMLOutputter
  */
-
 class MessageForm extends Form
 {
     /**
      * User to send a direct message to
      */
-
     var $to = null;
 
     /**
      * Pre-filled content of the form
      */
-
     var $content = null;
 
     /**
@@ -68,7 +65,6 @@ class MessageForm extends Form
      * @param User          $to      user to send a message to
      * @param string        $content content to pre-fill
      */
-
     function __construct($out=null, $to=null, $content=null)
     {
         parent::__construct($out);
@@ -82,7 +78,6 @@ class MessageForm extends Form
      *
      * @return string ID of the form
      */
-
     function id()
     {
         return 'form_notice-direct';
@@ -93,7 +88,6 @@ class MessageForm extends Form
      *
      * @return string class of the form
      */
-
     function formClass()
     {
         return 'form_notice ajax-notice';
@@ -104,7 +98,6 @@ class MessageForm extends Form
      *
      * @return string URL of the action
      */
-
     function action()
     {
         return common_local_url('newmessage');
@@ -117,6 +110,7 @@ class MessageForm extends Form
      */
     function formLegend()
     {
+        // TRANS: Form legend for direct notice.
         $this->out->element('legend', null, _('Send a direct notice'));
     }
 
@@ -125,7 +119,6 @@ class MessageForm extends Form
      *
      * @return void
      */
-
     function formData()
     {
         $user = common_current_user();
@@ -133,7 +126,9 @@ class MessageForm extends Form
         $mutual_users = $user->mutuallySubscribedUsers();
 
         $mutual = array();
-        // TRANS Label entry in drop-down selection box in direct-message inbox/outbox. This is the default entry in the drop-down box, doubling as instructions and a brake against accidental submissions with the first user in the list.
+        // TRANS: Label entry in drop-down selection box in direct-message inbox/outbox.
+        // TRANS: This is the default entry in the drop-down box, doubling as instructions
+        // TRANS: and a brake against accidental submissions with the first user in the list.
         $mutual[0] = _('Select recipient:');
 
         while ($mutual_users->fetch()) {
@@ -150,6 +145,7 @@ class MessageForm extends Form
             $mutual[0] = _('No mutual subscribers.');
         }
 
+        // TRANS: Dropdown label in direct notice form.
         $this->out->dropdown('to', _('To'), $mutual, null, false,
                              ($this->to) ? $this->to->id : null);
 
@@ -173,13 +169,13 @@ class MessageForm extends Form
      *
      * @return void
      */
-
     function formActions()
     {
         $this->out->element('input', array('id' => 'notice_action-submit',
                                            'class' => 'submit',
                                            'name' => 'message_send',
                                            'type' => 'submit',
+                                           // TRANS: Button text for sending a direct notice.
                                            'value' => _m('Send button for sending notice', 'Send')));
     }
 }
diff --git a/lib/messagelist.php b/lib/messagelist.php
index da7e9a6c27..0185977285 100644
--- a/lib/messagelist.php
+++ b/lib/messagelist.php
@@ -4,7 +4,7 @@
  * Copyright (C) 2011, StatusNet, Inc.
  *
  * The message list widget
- * 
+ *
  * PHP version 5
  *
  * This program is free software: you can redistribute it and/or modify
@@ -44,7 +44,6 @@ if (!defined('STATUSNET')) {
  * @license   http://www.fsf.org/licensing/licenses/agpl-3.0.html AGPL 3.0
  * @link      http://status.net/
  */
-
 abstract class MessageList extends Widget
 {
     var $message;
@@ -60,10 +59,10 @@ abstract class MessageList extends Widget
         parent::__construct($out);
         $this->message = $message;
     }
-    
+
     /**
      * Show the widget
-     * 
+     *
      * Uses newItem() to create each new item.
      *
      * @return integer count of messages seen.
@@ -74,6 +73,7 @@ abstract class MessageList extends Widget
 
             $this->out->elementStart('div', array('id' =>'notices_primary'));
 
+            // TRANS: Header in message list.
             $this->out->element('h2', null, _('Messages'));
 
             $this->out->elementStart('ul', 'notices messages');
@@ -85,7 +85,7 @@ abstract class MessageList extends Widget
                 if ($cnt > MESSAGES_PER_PAGE) {
                     break;
                 }
-                
+
                 $mli = $this->newItem($this->message);
 
                 $mli->show();
diff --git a/lib/messagelistitem.php b/lib/messagelistitem.php
index 44e6976454..ba8cf834af 100644
--- a/lib/messagelistitem.php
+++ b/lib/messagelistitem.php
@@ -4,7 +4,7 @@
  * Copyright (C) 2011, StatusNet, Inc.
  *
  * A single list item for showing in a message list
- * 
+ *
  * PHP version 5
  *
  * This program is free software: you can redistribute it and/or modify
@@ -65,7 +65,6 @@ abstract class MessageListItem extends Widget
      *
      * @return void
      */
-
     function show()
     {
         $this->out->elementStart('li', array('class' => 'hentry notice',
@@ -120,6 +119,7 @@ abstract class MessageListItem extends Widget
         if ($this->message->source) {
             $this->out->elementStart('span', 'source');
             // FIXME: bad i18n. Device should be a parameter (from %s).
+            // TRANS: Followed by notice source (usually the client used to send the notice).
             $this->out->text(_('from'));
             $this->showSource($this->message->source);
             $this->out->elementEnd('span');
@@ -129,6 +129,29 @@ abstract class MessageListItem extends Widget
         $this->out->elementEnd('li');
     }
 
+    /**
+     * Dummy method. Serves no other purpose than to make strings available used
+     * in self::showSource() through xgettext.
+     *
+     * @return void
+     */
+    function messageListItemDummyMessages()
+    {
+        // A dummy array with messages. These will get extracted by xgettext and
+        // are used in self::showSource().
+        $dummy_messages = array(
+            // TRANS: A possible notice source (web interface).
+            _m('SOURCE','web'),
+            // TRANS: A possible notice source (XMPP).
+            _m('SOURCE','xmpp'),
+            // TRANS: A possible notice source (e-mail).
+            _m('SOURCE','mail'),
+            // TRANS: A possible notice source (OpenMicroBlogging).
+            _m('SOURCE','omb'),
+            // TRANS: A possible notice source (Application Programming Interface).
+            _m('SOURCE','api'),
+        );
+    }
 
     /**
      * Show the source of the message
@@ -142,7 +165,7 @@ abstract class MessageListItem extends Widget
      */
     function showSource($source)
     {
-        $source_name = _($source);
+        $source_name = _m('SOURCE',$source);
         switch ($source) {
         case 'web':
         case 'xmpp':
diff --git a/lib/microappplugin.php b/lib/microappplugin.php
index 0266f5184c..cd325560d3 100644
--- a/lib/microappplugin.php
+++ b/lib/microappplugin.php
@@ -4,7 +4,7 @@
  * Copyright (C) 2011, StatusNet, Inc.
  *
  * Superclass for microapp plugin
- * 
+ *
  * PHP version 5
  *
  * This program is free software: you can redistribute it and/or modify
@@ -39,8 +39,8 @@ if (!defined('STATUSNET')) {
  *
  * This class lets you define micro-applications with different kinds of activities.
  *
- * The applications work more-or-less like other 
- * 
+ * The applications work more-or-less like other
+ *
  * @category  Microapp
  * @package   StatusNet
  * @author    Evan Prodromou <evan@status.net>
@@ -48,7 +48,6 @@ if (!defined('STATUSNET')) {
  * @license   http://www.fsf.org/licensing/licenses/agpl-3.0.html AGPL 3.0
  * @link      http://status.net/
  */
-
 abstract class MicroAppPlugin extends Plugin
 {
     /**
@@ -255,10 +254,9 @@ abstract class MicroAppPlugin extends Plugin
      * by calling the overridable $this->deleteRelated().
      *
      * @param Notice $notice Notice being deleted
-     * 
+     *
      * @return boolean hook value
      */
-
     function onNoticeDeleteRelated($notice)
     {
         if ($this->isMyNotice($notice)) {
@@ -277,7 +275,6 @@ abstract class MicroAppPlugin extends Plugin
      *
      * @fixme WARNING WARNING WARNING this closes a 'div' that is implicitly opened in BookmarkPlugin's showNotice implementation
      */
-
     function onStartShowNoticeItem($nli)
     {
         if (!$this->isMyNotice($nli->notice)) {
@@ -294,9 +291,9 @@ abstract class MicroAppPlugin extends Plugin
         $nli->showNoticeLocation();
         $nli->showContext();
         $nli->showRepeat();
-        
+
         $out->elementEnd('div');
-        
+
         $nli->showNoticeOptions();
 
         return false;
@@ -310,7 +307,6 @@ abstract class MicroAppPlugin extends Plugin
      *
      * @return boolean hook value
      */
-     
     function onStartActivityObjectFromNotice($notice, &$object)
     {
         if ($this->isMyNotice($notice)) {
@@ -329,7 +325,6 @@ abstract class MicroAppPlugin extends Plugin
      *
      * @return boolean hook value
      */
-
     function onStartHandleFeedEntryWithProfile($activity, $oprofile)
     {
         if ($this->isMyActivity($activity)) {
@@ -337,7 +332,8 @@ abstract class MicroAppPlugin extends Plugin
             $actor = $oprofile->checkAuthorship($activity);
 
             if (empty($actor)) {
-                throw new ClientException(_('Can\'t get author for activity.'));
+                // TRANS: Client exception thrown when no author for an activity was found.
+                throw new ClientException(_('Cannot get author for activity.'));
             }
 
             $object = $activity->objects[0];
@@ -368,31 +364,32 @@ abstract class MicroAppPlugin extends Plugin
     function onStartHandleSalmonTarget($activity, $target)
     {
         if ($this->isMyActivity($activity)) {
-
             $this->log(LOG_INFO, "Checking {$activity->id} as a valid Salmon slap.");
 
             if ($target instanceof User_group) {
                 $uri = $target->getUri();
                 if (!in_array($uri, $activity->context->attention)) {
-                    throw new ClientException(_("Bookmark not posted ".
-                                                "to this group."));
+                    // @todo FIXME: please document (i18n).
+                    // TRANS: Client exception.
+                    throw new ClientException(_('Bookmark not posted to this group.'));
                 }
             } else if ($target instanceof User) {
                 $uri      = $target->uri;
                 $original = null;
                 if (!empty($activity->context->replyToID)) {
-                    $original = Notice::staticGet('uri', 
-                                                  $activity->context->replyToID); 
+                    $original = Notice::staticGet('uri',
+                                                  $activity->context->replyToID);
                 }
                 if (!in_array($uri, $activity->context->attention) &&
                     (empty($original) ||
                      $original->profile_id != $target->id)) {
-                    throw new ClientException(_("Object not posted ".
-                                                "to this user."));
+                    // @todo FIXME: Please document (i18n).
+                    // TRANS: Client exception.
+                    throw new ClientException(_('Object not posted to this user.'));
                 }
             } else {
-                throw new ServerException(_("Don't know how to handle ".
-                                            "this kind of target."));
+                // TRANS: Server exception thrown when a micro app plugin uses a target that cannot be handled.
+                throw new ServerException(_('Do not know how to handle this kind of target.'));
             }
 
             $actor = Ostatus_profile::ensureActivityObjectProfile($activity->actor);
@@ -422,7 +419,6 @@ abstract class MicroAppPlugin extends Plugin
      *
      * @return boolean hook value
      */
-
     function onStartAtomPubNewActivity(&$activity, $user, &$notice)
     {
         if ($this->isMyActivity($activity)) {
@@ -451,7 +447,6 @@ abstract class MicroAppPlugin extends Plugin
      *
      * @return boolean hook value
      */
-
     function onStartImportActivity($user, $author, $activity, $trusted, &$done)
     {
         if ($this->isMyActivity($activity)) {
diff --git a/lib/noticelistitem.php b/lib/noticelistitem.php
index 5942415c51..aafa935140 100644
--- a/lib/noticelistitem.php
+++ b/lib/noticelistitem.php
@@ -4,7 +4,7 @@
  * Copyright (C) 2010, StatusNet, Inc.
  *
  * An item in a notice list
- * 
+ *
  * PHP version 5
  *
  * This program is free software: you can redistribute it and/or modify
@@ -348,15 +348,20 @@ class NoticeListItem extends Widget
         if (empty($name)) {
             $latdms = $this->decimalDegreesToDMS(abs($lat));
             $londms = $this->decimalDegreesToDMS(abs($lon));
-            // TRANS: Used in coordinates as abbreviation of north
+            // TRANS: Used in coordinates as abbreviation of north.
             $north = _('N');
-            // TRANS: Used in coordinates as abbreviation of south
+            // TRANS: Used in coordinates as abbreviation of south.
             $south = _('S');
-            // TRANS: Used in coordinates as abbreviation of east
+            // TRANS: Used in coordinates as abbreviation of east.
             $east = _('E');
-            // TRANS: Used in coordinates as abbreviation of west
+            // TRANS: Used in coordinates as abbreviation of west.
             $west = _('W');
             $name = sprintf(
+                // TRANS: Coordinates message.
+                // TRANS: %1$s is lattitude degrees, %2$s is lattitude minutes,
+                // TRANS: %3$s is lattitude seconds, %4$s is N (north) or S (south) depending on lattitude,
+                // TRANS: %5$s is longitude degrees, %6$s is longitude minutes,
+                // TRANS: %7$s is longitude seconds, %8$s is E (east) or W (west) depending on longitude,
                 _('%1$u°%2$u\'%3$u"%4$s %5$u°%6$u\'%7$u"%8$s'),
                 $latdms['deg'],$latdms['min'], $latdms['sec'],($lat>0? $north:$south),
                 $londms['deg'],$londms['min'], $londms['sec'],($lon>0? $east:$west));
@@ -366,6 +371,7 @@ class NoticeListItem extends Widget
 
         $this->out->text(' ');
         $this->out->elementStart('span', array('class' => 'location'));
+        // TRANS: Followed by geo location.
         $this->out->text(_('at'));
         $this->out->text(' ');
         if (empty($url)) {
@@ -414,10 +420,11 @@ class NoticeListItem extends Widget
         $ns = $this->notice->getSource();
 
         if ($ns) {
-            $source_name = (empty($ns->name)) ? ($ns->code ? _($ns->code) : _('web')) : _($ns->name);
+            $source_name = (empty($ns->name)) ? ($ns->code ? _($ns->code) : _m('SOURCE','web')) : _($ns->name);
             $this->out->text(' ');
             $this->out->elementStart('span', 'source');
             // FIXME: probably i18n issue. If "from" is followed by text, that should be a parameter to "from" (from %s).
+            // TRANS: Followed by notice source.
             $this->out->text(_('from'));
             $this->out->text(' ');
 
@@ -434,7 +441,6 @@ class NoticeListItem extends Widget
             // if $ns->name and $ns->url are populated we have
             // configured a source attr somewhere
             if (!empty($name) && !empty($url)) {
-
                 $this->out->elementStart('span', 'device');
 
                 $attrs = array(
@@ -479,6 +485,7 @@ class NoticeListItem extends Widget
                     array(
                     'href' => $convurl.'#notice-'.$this->notice->id,
                     'class' => 'response'),
+                    // TRANS: Addition in notice list item if notice is part of a conversation.
                     _('in context')
                 );
             } else {
@@ -513,6 +520,7 @@ class NoticeListItem extends Widget
 
             $this->out->elementStart('span', 'repeat vcard');
 
+            // TRANS: Addition in notice list item if notice was repeated. Followed by a span with a nickname.
             $this->out->raw(_('Repeated by'));
 
             $this->out->elementStart('a', $attrs);
@@ -539,7 +547,9 @@ class NoticeListItem extends Widget
                                           array('replyto' => $this->profile->nickname, 'inreplyto' => $this->notice->id));
             $this->out->elementStart('a', array('href' => $reply_url,
                                                 'class' => 'notice_reply',
+                                                // TRANS: Link title in notice list item to reply to a notice.
                                                 'title' => _('Reply to this notice')));
+            // TRANS: Link text in notice list item to reply to a notice.
             $this->out->text(_('Reply'));
             $this->out->text(' ');
             $this->out->element('span', 'notice_id', $this->notice->id);
@@ -565,7 +575,10 @@ class NoticeListItem extends Widget
                                           array('notice' => $todel->id));
             $this->out->element('a', array('href' => $deleteurl,
                                            'class' => 'notice_delete',
-                                           'title' => _('Delete this notice')), _('Delete'));
+                                           // TRANS: Link title in notice list item to delete a notice.
+                                           'title' => _('Delete this notice')),
+                                           // TRANS: Link text in notice list item to delete a notice.
+                                           _('Delete'));
         }
     }