The trial in a criminal case has to be in Thai only. Most Thai judges have a good command
of English, but they have to conduct the hearing in Thai. Sometimes, if an interpreter translates wrongly, the judge will instruct the translator to re-translate correctly.
The trial in a civil case in court must also be in Thai.
The hearing for arbitration in some civil cases can be conducted in English, if the related parties consent in an agreement from the very beginning before the dispute occurred.