Originally Posted by Boonmee

This is basically right. Although I would say that 90% of Thai conversations are about food (and therefore do not get particularly complicated), it is definitely the case that the dialogues are much more vague than in English. It is quite common, in my experience, for Thais to misconstrue what someone is saying to them, so that many conversations involve phrases like "You mean like this?", "In what way?", etc. ie questions which lead to a narrowing-down of the subject under discussion.

Originally Posted by Boonmee

For complicated English words (what we might call "advanced vocab") there are two possibilities in Thai. Firstly, Pali words. These are particularly used in religious and political contexts, for example Prachaathibtai (democracy), Aariyatham (civilisation), Samaati (meditation).
The second possibilty is a combination of words. Since this word has already come up, I'll use it as an example. "to inculcate (somebody) with (something)" = Plook fang (sing nai) hai kab (khon nai); lit: "Plant/build listening of something give with someone". "Claustrophobia" = Rohk klua jamkad boriwen (lit: disease of fear of limited bounds).

To summarise that more succinctly: whereas advanced English vocab is based around adaptations (even bastardisations) of Greek and Latin, Thai uses either pure Pali and Sanskrit, or combinations of "pure Thai" vocab.

Worth noting, too, that "pure Thai" vocab is largely monosyllabic, unlike Pali and Sanskrit which are Indo-European languages (putting them in the same family as most European languages, and Persian.)

I would suggest, therefore, that the reason Thais normally use quite vague, basic, vocab, is because otherwise sentences become very "wordy".