Site visitors from Thailand are asking to disable unicode - why, what could be wrong?

Question

Unicode

Good day.
There is a self-written website in Russian, English, Spanish and French.
Pages are given in utf-8. Visitors from different countries go and everything seems to be fine, they don’t complain. But! Visitors from Burma and Thailand periodically ask to turn off unicode (if google translate translates correctly).
What could be wrong?
What was checked:
There is a registration on the site, Thai characters are copied into the input fields normally, an account is created, etc.