Thanks for the case doc.
Based on marital agreement concluded in Switzerland, which is honoured in Thailand, I will not have conjugal but separated property. Else it could be argued that my pension income in Switzerland is conjugal property and transfers are partially a gift from my wife to herself.
With respect to joint tax filing, I consider it a little contradictory to claim THB 60k spouse allowance on the one side and keep the gift tax exempt on the other side.
I could organise myself with zero taxable income and provide respective documentation, but I consider to come up with a tax payable equal to the withholding tax on the interest on my Thai bank accounts, not reclaiming the withholding tax and hopefully keeping the tax man happy and less motivated for cumbersome inquiries.