it comes from the slavic word for germans - NEMTSI which comes from nemy ( meaning mute because slaves couldn't understand germanic languages ) the ottmans adopted in the Nemçe form and then arabic took it from turkish to AL-NIMSA form (النمسا).
@Muntasir Attamy, apparently Salvatore and myself are studying Arabic and aren’t total beginners but rather language learners with a certain amount of curiosity about the origin of words. Do you have some explanation to the question Salvatore raised?
Any idea why the name of Venice in Arabic is the same as rifle?