The maximum length of the missing strings to display can be set now. Fixes MDL-8184.

Because the tags <pre>...</pre> are used when displaying original English
version of missing texts, the screen may get very wide. This patch displays
only first 60 characters followed by '...'. This produces better output.

admin/lang.php

@@ -46,6 +46,7 @@
     define('LANG_DEFAULT_FILE', '');            // default file to translate. Empty allowed
     define('LANG_LINK_MISSING_STRINGS', 1);     // create links from "missing" page to "compare" page?
     define('LANG_DEFAULT_USELOCAL', 0);         // should *_utf8_local be used by default?
+    define('LANG_MISSING_TEXT_MAX_LEN', 60);    // maximum length of the missing text to display
 
     $mode        = optional_param('mode', '', PARAM_ALPHA);
     $currentfile = optional_param('currentfile', LANG_DEFAULT_FILE, PARAM_FILE);
@@ -199,6 +200,9 @@
                         $missinglinkstart = '';
                         $missinglinkend = '';
                     }
+                    if (strlen($value) > LANG_MISSING_TEXT_MAX_LEN) {
+                        $value = substr($value, 0, LANG_MISSING_TEXT_MAX_LEN) . ' ...';
+                    }
                     $o .= "$"."string['".$missinglinkstart.$key.$missinglinkend."'] = \"$value\";<br />";
                 }
             }