You get what you pay for a free language

[thrash]

Note that Words of Command in the Sorcerers' Tongue are effective regardless of whether one understands that language. I suspect that makes it a "philosophical" language, with potent ties to Reality (tm). That might make it difficult to express counter-factuals (without making them true somehow). This would also tie in with the idea (not from TFT, necessarily) of demons not being able to lie explicitly, however much they distort and deceive by other means.