Opera Mini allows users to change the default search engine, which is google.com in many regions. Wikipedia, Dictionary.com and IMDb are the other search engines available with Opera Mini. There may be some other search providers available to you depending upon your location.
Unfortunately, users can’t add more search engines to Opera Mini (see update below). But, one can edit the existing search engines and hence indirectly add new search engines.
To add a new search provider to Opera Mini / Opera Mobile, follow these steps:
Step #1: Tap the arrow icon in the search box (or, press the down key).
Step #2: Select "Manage Search Engines" option.
Step #3: Select any existing search engine to edit. Enter new title and address*. Save the settings.
Step #4: Now, make it your default search engine. For this, tap the arrow icon in the search box and select the edited search engine.
The address field in step #3 should be the URL for getting search results. Here are some examples:
For Google India: http://www.google.co.in/m?q=%s
For Twitter Search: http://search.twitter.com/search?q=%s
(‘%s’ will be replaced by your search query.)
Update: You can add new search engines to Opera Mini. See this comment and the screenshot below.