hi, is anyone know where i can install a thai language version for my handphone?

i bought a nokia 5800 in malaysia, and i wish to install thailand language to my handphone so that i can sms to my family in thai language.

but i have no idea where i can find this software or any handphone shop to do this for me.
and approximately how much.

i would appreciate if anyone can let me know this.

thank you!