If possible, It would be better if user can edit their custom search engine. (to instead of the Built-in engine)

like:
Google Translate：https://translate.google.com.tw/?hl=zh-TW#auto/zh-TW/{searchTerms}
Cambridge ：http://www.learnersdictionary.com/definition/{searchTerms}

or like: https://i.imgur.com/Wr4O2GF.png