Hi, I'm afraid your question is a bit generic. First of all, what search are you using? Did you install some extensions and/or configure something? If not, what database are you using?
MediaWiki definitely supports Chinese search in English wikis, e.g. https://meta.wikimedia.org/wiki/Special:Search/%E5%88%A4%E4%BE%8B%E9%AB%94%E5%88%B6. Nowadays all search efforts are being spent on this extension, which you're encouraged to try: https://www.mediawiki.org/wiki/Extension:CirrusSearch
Finally, unless you're using Translate, your wiki is certainly doing multilingualism wrong and no fancy things are really possible, because MediaWiki is quite silly about it. Hopefully 1.25 will be better and there are some features you can already test: * https://bugzilla.wikimedia.org/show_bug.cgi?id=9360 * https://bugzilla.wikimedia.org/show_bug.cgi?id=54832
Nemo