How can I manage tax obligations while on a NON-O volunteer visa in Thailand with foreign income?

Youre in a legal jungle with your situation, wish you best of luck boyo

Simple answer, claim you're a German tax resident and pay tax there, ignore the Thai side, it's highly unlikely to be an issue. If you don't move that money to Thailand in the same year, you aren't required to pay tax on it here anyways. (they aren't gonna know where the money originated anyways)

Complicated answer, living more than 180days in Thailand, you would likely be classed as a tax resident, if you're bringing money into the country and working here you should probably be paying tax on it here. How that affects your visa, I have no idea. If you want to pay tax in Thailand, talk to an accountant at a firm which also has visa lawyers.

Are you referring to the double taxation treaty? If so I think you may be misunderstanding it.

If your income is Germany source income and paid to you in Germany then it's taxable in Germany regardless of your tax residency status there. This concept applies pretty much worldwide.

Umm, I'm confused. Volunteering means you are not being paid. Also, where you are volunteering gives you all the paperwork for extensions, and work permit.

If you are doing work in Thailand, then yes you file and pay taxes, no matter where the pay comes from. Go to your local revenue office and get a tax ID number. File your taxes on , I believe, form 91, or if your situation warrants it, then form 92. When you go to your local revenue office and file your return, you get a receipt. That is what you need for your work permit renewal.

The person you need to speak to is your foundation's accountant. They will know ( or should know) what is required.