The best place to check out what is on T5 is
http://www.lyngsat.com/t5.shtml
As far as I know, the currently FTA channels are:
TGN -
Thai
TGN Radio (Bangkok 94 FM) - Thai
NAT - Thai, Lao, and soon some others.
VT4 -
Vietnamese
CTN - Cambodian
Japan, Korean, Chinese...