I noticed the following in the release notes:
Keyboard: include words from all active locales in spell checking to support multiple locales again after the port to Android 14
However, I am still getting red lines from the spell checker when I switch the language of my keyboard to anything other than the primary language that my phone is set to. Does this only fix this behaviour when using the native GrapheneOS keyboard? I am using OpenBoard so maybe that's why it hasn't been fixed for me.