From my experience, swearing seems to be one of the last few things you acquire when getting competent in a foreign language. (Ignoring the fun “Teach me some swears!” pastime of a beginner—they learn the words but not how to use them.) In my time working as a programmer, most of my coworkers have been non-native English speakers, and I don’t think it’s a coincidence that the ones who swear the most are also the most generally proficient in English.

Most of those top few are also native speakers of languages that are closely related to English, such as German, Dutch, and French, but curiously, the one who curses the most, and the most proficiently, is Israeli.