Any Thai who's spent a day in school anywhere in this country was taught Central Thai (the government approved version of Thai). Now whether they speak that at home is another story, but believe me they know how to speak, read, and write Central Thai. That's because EVERYTHING in print, all the radio shows (except those cheesy bootleg AM stations up-country) and all the television programming use only Central Thai.
The Thais my age (mid-50's) used to get around 6 years of schooling, yet even they can read, write and speak just fine.
In some ways Thai is no different than English as far as infrequently used or spelled words and the "jargon jungle" a person experiences with different trades. It's highly unlikely I could wade thru a lengthy business contract or understand convoluted tax laws in English yet I'm a native American English speaker, born, bred and corn fed.
I will concede that there's a marked difference between ภาษาราชการ (government language) often called ภาษาทางการ (formal language), ภาษาภาษี (tax language), ภาษาเขียน (written language), ภาษาปาก (spoken language) and ภาษาท้องถิ่น (regional dialects), but that's not all too different from English. If a person is unlikely to have use for the vocab, they forget it or just plain don't learn it.
The point I was trying to make with my oh-so "cryptic observation" was; if the Thais can speak, read and write Thai so can ANY foreigner, if they really want to.
