How to encode UTF-8

can anyone tell me how to convert a string of Unicode or Big5 or (any asian
multi-byte character string) into UTF-8?

I need to produce an XML document which include some chinese characters, but
I don't know how to encode it in UTF-8 format.

The Wikipedia description is a bit too complex. Any existing code on the
net?

I check Indy source and it only has TidUTF8Decoder class but not encoder.

thanks  a lot.

Dennis