Hello,
The Hindi and Kannada Wikipedias use JavaScript to do that; for
example, try typing in the box at
<http://hi.wikipedia.org/wiki/test?action=edit>.
The interface has also been translated into Hindi, Tamil, and Kannada.
You can set the interface language in the file LocalSettings.php
(globally) or through the wiki page "Special:Preferences" (per user).
Yours cordially,
Jesse Martin (Pathoschild)