Automatically switch spell check language/dictionary as you type in Firefox

I have been looking for a plugin like this for ages. I constantly switch between Swedish and English when I work and it’s a pain to always remember to switch the spell check to the correct language. But today I found Dictionary Switcher that automatically sets the spelling language to the locale of the page but also detects what language you are typing in and switch to the correct language. I’ve made a YouTube Video to show how it works.