so, I attempted to be a little more thorough in my testing, and tried words that could be more commonly misspelled in both English and Indonesian, here I use “karna” (shorthand “karena”, but it isn’t in the dictionary so it shows suggestions), which could be “karma” (EN), or “karena, warna, karya” (ID).

Here, it displays results from both languages, but as we saw with “amongt”, there were also suggestions from both languages. They just weren’t showing both ID and EN suggestions.
I’m starting to suspect that this is going to turn into a wild goose chase (since you said Obsidian uses Google spellchecking) - and I’ll just have to live with it - but if maybe a dev or someone equally knowledgeable could shed a little light on this, it would be super appreciated.