Adding Latvian or another language in Pages for spelling correction.

Hello!

I am really concerned about auto-correction and checking spelling for the Latvian language in Pages.

As I am looking in General settings > Keyboard (I've added Latvian), but when I am writing in Pages in Latvian - unfortunately, spelling isn't checked, because there's no such language available (Keyboard > Input sources> Spelling > and no Latvian). Maybe you know how to add Latvian or any other language that is not in the list? It's my first experience with MacOS. Would like to enjoy and understand it, all in all. Would really appreciate your help.