That's applicable to pretty much every single developer out there not born in an English speaking country. Which just so happens to be my case.

Why not also translate classes', functions' and variables' names too?

I am not a native English speaker. I also really don't have any resources, wether time, money or mental bandwidth to waste on translation.

Nearly all code and documentation out there is in one single language, that happens to be English, so I work in English, and I wouldn't have it any other way.