Yes, I've done it too (I am a french native). Especially common is writing code in English and commenting in ones native language. There are other cases, like when the english word is not known or to stay consistent with a data source.

I've also seen the native word to avoid conflicts, like adding "2" at the end of a variable. That's bad, don't do it kids ;)

But here, the "hero" has a "speed" while the "ennemi" (french for "enemy") has a "vitesse" (french for "speed"). That's why I thought that the enemy is more likely to be a later, less supervised addition.

And BTW, I didn't notice any french swear word in that code. That kid is more mature than I was :)

It can also go the other way, of course (variables in native language, or just single-letter variables, and comments in English). I seem to remember that Linus Torvalds commented all of his code in English without ever thinking about it.

Even in a professional context it's reasonable to use the language your customer (business expert) is using. Beware of mapping technical terminology into another language! And if that means you write Swedish code, that's perfectly valid.

I've definitively had the case of having all the codebase in English (not our native language), since all concepts mapped easily, and then a new concept appears and damned if I know how to translate it! So now we're stuck with a single non-English term in the codebase, which is a blot on the whole work :(