I don't understand.

American Sign Language:
I http://commtechlab.msu.edu/sites/aslweb/I/W1706.htm
don't http://commtechlab.msu.edu/sites/aslweb/D/W0982.htm
comprehend. http://commtechlab.msu.edu/sites/aslweb/C/W0705.htm

English:
I don't understand.

French:
Je ne comprends pas.

Italian:
Non capisco.

Spanish:
No comprendo.

Swahili:
Hapana, sielewi.