Violentmonkey

Violentmonkey provides userscripts support for Chromium-based Opera.
Violentmonkey for Opera Presto: https://github.com/gera2ld/Violentmonkey-oex

Multiple language

There are two ways to help with the translations:

(Recommended) Go to http://cotrans.geraldl.net, and translate the desired language.
You may also download src/_locales/en/messages.json and translate it into your own language, and then make a pull request.