Fix missing localization of HTML editor when assets_dir != INSTALL_PATH

Conflicts:
	CHANGELOG

CHANGELOG

@@ -3,6 +3,7 @@ CHANGELOG Roundcube Webmail
 
 - Searching in both contacts and groups when LDAP addressbook with group_filters option is used
 - Use contact_search_name format in popup on results in compose contacts search
+- Fix missing localization of HTML editor when assets_dir != INSTALL_PATH
 - Fix message list multi-select/deselect issue (#5219)
 - Fix bug where contact search menu fields where always unchecked in Larry skin
 - Fix XSS issue in href attribute on area tag (#5240)

program/include/rcmail.php

@@ -1867,13 +1867,14 @@ class rcmail extends rcube
         }
 
         $lang_codes = array($_SESSION['language']);
+        $assets_dir = $this->config->get('assets_dir') ?: INSTALL_PATH;
 
         if ($pos = strpos($_SESSION['language'], '_')) {
             $lang_codes[] = substr($_SESSION['language'], 0, $pos);
         }
 
         foreach ($lang_codes as $code) {
-            if (file_exists(INSTALL_PATH . 'program/js/tinymce/langs/'.$code.'.js')) {
+            if (file_exists("$assets_dir/program/js/tinymce/langs/$code.js")) {
                 $lang = $code;
                 break;
             }