Drupal 7 doesn't allow search in chinese character I'm using drupal 7 multilanguage site. When I enter chinese character (UTF8) in search box and search, it gives error like below: 

Bad Request

Your browser sent a request that this server could not understand.

Additionally, a 403 Forbidden error was encountered while trying to use an ErrorDocument to handle the request.

Can I know what's the problem and how to solve it?

Thank you in advance.
This is probably a server configuration issue.  I have successfully used Japanese search on both Drupal 6 and 7.  Try installing a copy of your site on a local development environment (Acquia Dev Desktop, etc.) and see if the problem recurs.