Improve language feature

Imported from UserVoice

Author: XeonCat

I have set up both the UI and Document language to US English, but whenever I try to write a new paragraph, the new text language is in my Keyboard Layout language, Portuguese, and so I have to select the text and set it to US English again for the spellchecker to work.

Solution: Force writing in the Document Language whenever new things are being written, thank you.