Same here. I always set everything to en_US, because that's the native language of computing. Any time I've had to use something in my native language (Polish), the translation was terrible - and the only reason I was not confused was because I could mentally untranslate the Polish text to the most likely English original.

Speaking of computing and translations: the most annoying case I've had was not with UIs, but with books. Back in the day, I bought two C++ books by Scott Meyers (Effective C++ and More Effective C++), both published in Polish, and each by a different publisher. In the first one, they translated "template" -> "szablon" and "pattern" -> "wzorzec", and in the other, they translated "template" -> "wzorzec" and "pattern" -> "szablon". Took my teenage mind quite a while to make sense of the confusion.