Thanks. I didn't think to look in the Edit menu but that makes sense.
It's not exactly what I was looking for, but I can see that FMP is predicated on using only one language at a time, so the thing I was looking for doesn't really work.
I'll consider submitting the other things as a feature request/suggestion, i.e. give a specific object a language property, not just trigger a script to change FMP's language.
I'm running into the same issue (in my case I've created a database to learn Spanish so naturally, there are some fields are Spanish, others English). For this DB spelling correction is very helpful in Spanish fields, annoying (since incorrect) in English.
The thing that's especially confusing, is that you ARE able (via Storage Tab of field Options Dbox) to set the default Language for each field. individually. It says "Applies to text indexing, sorting and default display font" So why not spelling?
I'd thought there was at least some way to turn off the red underline/spell check for select fields, but perhaps this was in my imagination.