Language change doesn't trigger recomputation of stateful language-related functions

[lognaturel]

https://forum.getodk.org/t/jr-choice-name-not-re-evaluated-on-form-language-change/40353

• Changing language doesn't immediately trigger recomputation
• When a form first is launched, the default language is used even if it's not meant to be the current language

I haven't dug any deeper. The first step would be to get some tests in.