Direct at Luxembourg Embassy: Good news – Luxembourg has an Embassy in Bangkok, and you can apply directly at the consular section by appointment. They don’t use VFS. Email or call them to schedule a visa appointment (usually within a week or two). The process is a bit more personal since it’s a small embassy; expect possibly a short chat when you submit documents.
Small volume, detailed check: Because Luxembourg processes fewer visas, they often check documents very thoroughly. Use their official checklist (available on the embassy’s site). Pay special attention to employment letters and translations – they might want any Thai documents (like marriage certificate or similar) translated to English or French/German. An invitation letter from your partner in Luxembourg is a must, and it should be detailed (they can mention how long you’ve been together, etc.). The letter can be in English or French.
Financial & sponsorship: Luxembourg will want to see you have enough money. If your European partner (maybe working in Luxembourg) sponsors you, include their financial proof and a formal sponsorship letter. However, be prepared to show personal funds as well. The country is affluent, so demonstrating financial sufficiency is important.
Return ties focus: The embassy will likely ask for proof of ties (they specifically mention in guidance that strong ties help). Show your work contract, business registration, or family documents. They might even ask how you plan to use the visa (they can ask if you intend to travel elsewhere in Schengen, etc.). Just be honest – say you plan to spend most time in Luxembourg with your partner and maybe short trips around, then return to Thailand. With complete paperwork, Luxembourg is known to issue visas reliably.