You can also do a Google account wide change through your account settings to use your language interface across many Google services like Gmail and Youtube.
Many Tamil Wikipedians have noted that Tamil Wikipedia articles are shown at the top of the search results even when the keyword is in English.
This is not the case for every search but we guess that the quality of the article, presence of the keyword in English at the beginning of the article and accessing your language Wikipedia from an Indian IP address often can contribute to this scenario.
When many users show trust in native language articles, the articles will gain more trust in Google's view and it will start pushing for general audience too.
Right now, lack of awareness of native language Wikipedias is an important issue.