Have a nice day!

American Sign Language:
Have (a) http://commtechlab.msu.edu/sites/aslweb/H/W1582.htm
nice http://commtechlab.msu.edu/sites/aslweb/N/W2496.htm
day! http://commtechlab.msu.edu/sites/aslweb/D/W0846.htm

English:
Have a nice day!

French:
Bonne journée!

Italian:
Buona giornata!

Spanish:
Espero que tengas un buen día.

Swahili:
Siku njema!