Every few months I come by and check on the status on this issue, only to find multiple threads about it with the same excuse. It's been going on for over a year already, but it seems Opera hasn't yet found a way to make it happen, which makes it seem there hasn't been an attempt to provide a fix, which is what makes it discouraging considering all other browsers let you add search engines. You'd think a Scandinavian company like Opera would be most interested in freedom to appeal to new users. Happy users recommend Opera, which brings you even more Google dollars. A few possible ideas:
a) make it so search engines have to be manually typed-in in settings - don't allow extensions/websites to add them.
b) have a section in the AddOns website where only pre-approved search engines can be added.
c) make it like unknown source extension installation - added search engines have to be manually approved in the search engine preference section.
d) if none of these ideas work, at the very least add more search engine options. at least one privacy-focused search engine (DuckDuckGo or Startpage, for example) would be welcome.
edit: hehe. nice to see lots of oldtimer My Opera era "server monkeys" around here.