Yes, Discord translates by default.
You can disable it easily
You can declare which language you can read without translation in your profile.
The translations seem good.
Yet I disabled automatic translation in my Discourse Account because I don’t like seeing something that is not what people wrote, presented as if it is. I can still have things translated on demand.
Example of good translation
I initially quoted here passages from Introducing R‑GX GDK - #24 by Gryzor and Introducing R‑GX GDK - #25 by XeNoMoRPH but because of the very effect discussed here they would be translated again for most users, preventing from seeing the actual quotes. So, for people who have translation enabled I’ll show a screen capture instead:
I other words, @Gryzor used an English expression that literally refers to a cow (animal) that is “holy”, and @XeNoMoRPH saw a Spanish expression that literally says “my mother” but is a totally relevant translation in the context (I would say “cromulent” to quote Homer Simpson but that might add to the confusion).
This is not basic translation. This is strong translation by a machine that knows about idiomatic expressions in various language and when to apply that knowledge.
We all live in a yellow submarine AI-translated forum 
It’s funny to realize that if you didn’t disable translation, when viewing any topic in this Discourse instance, including “for or against AI use”, what people wrote is examined by an AI and translated by it. So, you’re not actually reading what other people wrote, you’re reading AI-generated text.
Extra
A caricature what can happen when machines change what people write was published on xkcd: New Phone Thread and explained on 2015: New Phone Thread - explain xkcd .