In MediaWiki 1.17 (and newer versions) the title for the language links is missing. PHP prints the following message:
PHP Notice: Undefined index: title in skins/Vector.php on line 646
See http://www.mediawiki.org/wiki/Extension_talk:Polyglot#MediaWiki_1.17_using_vector-Skin:_Undefined_index:_title for details and solution.
Version: unspecified
Severity: normal