Right now, if I select something and do a right click, the only search option I see is
Search Google for 'whatever I selected'
For example:

How do I add more search engines to this list?
Right now, if I select something and do a right click, the only search option I see is
Search Google for 'whatever I selected'
For example:

How do I add more search engines to this list?
I am using this extension: https://chrome.google.com/extensions/detail/ocpcmghnefmdhljkoiapafejjohldoga
You can't add additional search engines, but you can change which search engine it uses. Setting the default search to Yahoo would then allow you to search Yahoo for the selected text. I think being able to add additional search engines to this list would be a great idea though, so I have added it as a feature request.
The only alternatives would be to use a bookmarklet like the one created for Wikipedia or to use a Google Chrome Extension, however both of these options would require clicking on a link or button instead of right clicking on the text.
Context Menu Search Google Chrome Extension would allow you to have any website as search engine. A detailed how to can be found at - Customize Google Chrome Context Menu.