For a simple way to add Wikpedia into Chrome as a search engine follow the below steps:

in Chrome go to Tools menu, then Options, and in the Default Search section click Manage

then click Add and enter the below details in the available fields

Name: Wikipedia

Keyword: wiki

URL: http://en.wikipedia.org/wiki/%s

refer image below:

No in chrome just type wiki followed by where you want, ie 'wiki php' in the chrome address box (refer image below) and chrome will now search wikipedia for that term