I am writing notes in several languages. Since it is only possible to use the system language for the spell check in the macOS version I can’t spellcheck several languages.
Proposed solution
Set a default spell check language (e.g. system language) but make it possible to set the language of a specific document or even paragraph.
I like this idea a lot - or at least, if not note by note, to choose multiple languages so it knows to not mark words as misspelled! If Google can translate itself to Spanish based on my IP address without me asking, surely Obsidian can do Polish if I SPECIFICALLY ask.