You are welcome. (as a response to "Thank you.")

American Sign Language:
Welcome. http://commtechlab.msu.edu/sites/aslweb/W/W4447.htm

English:
You are welcome.

French:
Je vous en prie.

Italian:
Prego.

Spanish:
De nada.

Swahili:
Hakuna matata. (means: No problem. Responses to "thank you" are generally not used. However, this is an acceptable response.)