sigeena

Teochew is also spoken in Singapore and Malaysia as well. In both places, it also faces the end of life, as most of the younger generation do not use it as frequently as before. Teochew is not mutually intelligible with Mandarin. Primarily, because Mandarin is a northern dialect whereas Teochew is a southern dialect. Teochew is closer to Hokkien, and these 2 dialects are almost 70-80% mutually intelligible.

Teochew is probably still taught in Thailand, but you'll need to find a Clan Clubhouse of sorts to find some kind of teaching. I doubt they'll use the current Simplified Script to teach Teochew, since most of the literature will probably be in Traditional Script. Using Thai to learn Teochew will only learn the superficial aspects of Teochew, since Teochew has about ?6? tones. And not all the consonants will be transmitted 100%.

Most of Teochew can be heard in Yaowaraj  and it's also beginning to be pretty common to hear the traders there speak in Mandarin as well. I believe that Bangkok is seeing a growing trend of Chinese tourists from mainland China in the past 5 years.

In the past (40's-60's), most of the language was transmitted orally. Only a few learned ones, or traders, would be able to read and write. These learned ones would then be able to make a living of sorts reading and writing letters. I doubt many Thais are able to speak Teochew comprehensively. The older generation yes, but the current one less likely.

I doubt its relative use in the modern world.

Wiki

There's a number of external links at the end of the wiki page which should be useful.