make list of 'Languages that support variant conversion' dynamic

see bug 33223. Placing this list in LanguageConverter,
so people see the list, when adding new Converters

Change-Id: I088bc1f0ea01d7d6e02c736261311919a0956a57

includes/api/ApiQuery.php

@@ -690,7 +690,7 @@ class ApiQuery extends ApiBase {
 					'NOTE: generator parameter names must be prefixed with a \'g\', see examples' ),
 			'redirects' => 'Automatically resolve redirects',
 			'converttitles' => array( "Convert titles to other variants if necessary. Only works if the wiki's content language supports variant conversion.",
-					'Languages that support variant conversion include gan, iu, kk, ku, shi, sr, tg, zh' ),
+					'Languages that support variant conversion include ' . implode( ', ', LanguageConverter::$languagesWithVariants ) ),
 			'indexpageids' => 'Include an additional pageids section listing all returned page IDs',
 			'export' => 'Export the current revisions of all given or generated pages',
 			'exportnowrap' => 'Return the export XML without wrapping it in an XML result (same format as Special:Export). Can only be used with export',

languages/LanguageConverter.php

@@ -29,6 +29,23 @@
  * @maintainers fdcn <fdcn64@gmail.com>, shinjiman <shinjiman@gmail.com>, PhiLiP <philip.npc@gmail.com>
  */
 class LanguageConverter {
+
+	/**
+	 * languages supporting variants
+	 * @since 1.20
+	 * @var array
+	 */
+	static public $languagesWithVariants = array(
+		'gan',
+		'iu',
+		'kk',
+		'ku',
+		'shi',
+		'sr',
+		'tg',
+		'zh',
+	);
+
 	var $mMainLanguageCode;
 	var $mVariants, $mVariantFallbacks, $mVariantNames;
 	var $mTablesLoaded = false;