The g'moro in pshochim 3 says one should (generally) use 'nice' language, like not use the word 'tomai' but 'not tahor'. The g'moro in Eruvin 53b (the last line on the page) says that when a man is ...
Is it a Mitzva to speak Loshon Kodesh? (sources)
Is there a law against saying obscenities? If yes, what is considered obscene? Does it apply to any language or only to Hebrew?