If you don't mind the crashes, Gboard does this fine, generally detecting the difference between English, Spanish, and Portuguese for me. Although sometimes it wakes up on the wrong side of the bed and suggests only nonsense.

iOS autodetects and automatically switches languages as you described. The globe icon is just for switching key layouts. Language is independent of key layout.

> "Auto-Correction uses your keyboard dictionary to spellcheck words as you type, automatically correcting misspelled words for you." [1]

This is also consistent with my experience.

[1] https://support.apple.com/en-us/HT207525

If iOS has language detection like that, it's been broken for Finnish for years.

Looks pretty half-assed implementation to me. If they have autocorrect for Finnish, it shouldn't be too difficult to do quick lookups for both Finnish and English. And everyone knows that it's Autocorrect's carefully designed brand image to screw up, switching languages would allow more creative mistakes.