Much more importantly: Never ever auto-translate content to the user's language. Present what languages you actually have the data in. The user is smart enough to click the "translate" button in the web browser should they want. That translation is also likely to be better quality. English is not my first language. Or my second. But I understand it well enough to work in it every day. And I never ever want to wade th…
Machine translation has been good enough for a few years, that even native speakers don't notice it.
I often go through a few sentences or even entire paragraphs before stumbling onto something that doesn't make sense. And then I have to go back and reread everything.
Microsoft documentation is the worst offender. Their "some parts were translated automatically" notice is hard to, well, notice. And their translation is great! — until it doesn't work, because UI has different translation.