Interestingly enough, in Loshon Kodesh there are NO four letter words (any such obscenities come from the Arabic languages). Yiddish is another story.
Bad language reflects the inability on the part of its user, to speak intelligently using other words. If frum people are speaking that way, it is not only that they have absorbed the local vernacular, it is that they are too blase to speak English properly. JMO