I voted Russian because that is my language and I think it is great for many purposes.
BTW, Russian "swear language" or "words used when swearing" is called "mat". verb - "materitsya" (to mat )
you know how in the US some people, mostly girls, say "like" between any two words?
well, some guys in Russian school talk like that, only with mat throughout their speech instead of "like..like..like..like".
Here is a couple of jokes
(roughly remember that one)
Scientists discovered that one of the reasons Americans defeated the Japanese in WWII is because the average word in English is 4 letters long and the average word in Japanese has 10 letters. So americans could give orders much faster.
The average word in Russian is 6 letters long. However, when mat is used the effectivenes of speech is multiplied 2-3 times...
Another one:
Scientits invented a clock that moves 1 minute forward each time a swear word is heard. They put it in the office, after a day the clock moved 15 minutes. They put it in the army barracks: a soldier comes in and says: "It's cold as it is, what idiot put that fan on the wall?"
Denis