@aral Naturally my favourite is the #MediaWiki Translate extension, used on #translatewiki.net!
https://translatewiki.net/wiki/Translating:New_project
Ages ago, I and Nikerabbit wrote a comparison table for online translators:
https://docs.google.com/spreadsheets/d/e/2PACX-1vSo60fYYEsvYAXohAYSe_-C8YQIDvtKfzxi-gAwGcHU6uKANQCEB1Lo0RXmWWHfPhheGXEE4jxryrQJ/pubhtml