How far would you be willing to travel for the one build in LTR Dynamic ?

As a one-off? Wherever. If it turned into a relocation? Somewhere that has at least 30% English proficiency I think :'). TPE arrangements are a little spooky to consider in situations where you legitimately, actually can't help yourself if something goes wrong.

I'm happy to learn my partner's local language but some are just too difficult to conclusively say yes, I'll be able to learn this in a reasonable, safe timeframe. Or at least that's my personal consideration, I'm not super adept at foreign language learning (have my hands full with Swedish and that's about as easy as it gets). Most difficult I could manage would be Russian, I think? That's at least a semi-similar alphabet.