Not sure,
I'm a native English speaker, learned French, learned German, learned Spanish.
Learned a bit of Thai (+basic reading and writing) but never found it worthwhile.
Especially as I only get 1 year to stay at a time.
I've forgotten most of my German and Thai now as I never used them.
(my family speak Lanna and English)
If I had to learn another language now, it wouldn't be Thai as I don't live in Bangkok.
Always surprised at the western guys that insist you learn Thai while not seeming to understand that Central Thai isn't generally spoken by most Thai people in normal conversations.