Thailandish

I can't even say, "He's Thailandese," or "Thailandish." Or Siamese, which isn't right anymore and anyway sounds like a cat.

Source: wiktionary

The worst-hit economies were the Indonesian, Malaysian, Thailandish, Philippines and Korean ones.

Source: wiktionary

If, however, a prophet came from Siam — or must we say Thailand, and preached to me in Siamese or Thailandish, I should reject him, not because I did not like what he said, but because I could not make head or tail of it; […]

Source: wiktionary

Muslim friends in Bangkok are engaged on translating the book in^([sic]) Thailandish.

Source: wiktionary