Occasionally in Tehran, I meet someone from Bangkok (4)
I believe the answer is:
thai
'someone from bangkok' is the definition.
(Bangkok is in Thailand)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for thai that I've seen before include "Foreigner" , "eastern language" , "Asian tongue" , "Asian language" , "From Bangkok, for instance" .)