Getting Married in Thailand
https://th.usembassy.gov/u-s-citizen...d-in-thailand/
REGISTERING YOUR MARRIAGE IN THE USA: The United States generally recognizes the validity of marriages legally registered in Thailand. However, you cannot register your marriage in the United States through a U.S. Embassy, as marriage is a state-specific responsibility. If you would like to register your marriage in the United States, please contact the Attorney General in your state of residence for requirements. Some states may require your Thai marriage certificate to be certified. To certify a Thai marriage certificate, please have it translated into English and take both documents to the Thai Ministry of Foreign Affairs (MFA). Then make an appointment and bring the certified document to our office; we will authenticate the signature of the MFA officer for the appropriate fee.
Suspect each Embassy has similar information on their website?
I think there are two categories:
Thai citizen and foreigner
Two foreigners
and each represent different challenges re: documentation and "legality".
Most of the "two foreigner" marriage "events" held in Thailand, and this is a bit of an industry here, are actually legally done in a foreign country. There is no reason for the marriage to be legally recognized in Thailand.
The Thai citizen and foreigner marriage may need to be legally recognized in Thailand, especially if the couple plans to live in Thailand.