What should I do if I want to marry a Thai lady but don't have my birth certificate?

To marry a Thai national without a birth certificate, you can explore alternatives such as obtaining an 'Affirmation of Marital Status' from your embassy, which may only require a valid passport. Some commenters noted that a police clearance might also be necessary. If you still want a copy of your birth certificate, you can usually request one online or through your home country's birth registry. It's suggested that you also check directly with local authorities or your embassy for specific requirements and make sure to have any necessary documents stamped and translated as needed.