So you three may have localisation/internationalisation problems with RISC OS, I never disputed that. But this does not mean that RISC OS lacks the facilities to solve them. It just means, that no-one may have used the present facilities for that purpose. However discussions like this one drive new users away.
@Gulli: You are just describing the consequences of people not using the localisation/internationalisation facilities offered by RISC OS.
@Sawadee: Well, so you see that your problem has nothing to do with the technical capabilities of RISC OS, but with your lack of knowledge about the font system. Have you contacted EFF about this? They should have the knowledge you need. However they probably can not solve the problem themselves, because for that they would have to know something about the Thai language. And you may have to supply them with a Thai TrueType or Postscript font.
@egel: Yes, but how many of them speak English well enough not to need (or pay for the extra cost of) localised software?