It is interesting that after two world wars the stereotype of German was that of a hard and harsh language. I think Twain earlier take is more correct.
German is indeed a harsh language, filled with glottal stops and harsh consonants. The publicity doesn't help either, but it's mainly the phonemes.
Try to swear loudly and angrily in French, and try it in German. In German like you're cursing the world out of existence, in French it is like wiping your ass with silk.