This is the best language tool out there for Portuguese, Spanish and English. As I've only used with these three, I can only review for them.

This is a fantastic proof checker. It detects multiple languages, which is super convenient as I always jump between English and German text. Bonus points that it also supports German (Switzerland)

My most favorite feature is that I can actually run the local server on my PC and connect the add-on to my local server. I know that the devs don't take donations as it was too low But if there was, I would totally do that since I'm dodging the Premium feature with running it locally and I feel bad for it since this tool helps me a lot all the time!

Super!

Très rapide et utile, toujours là lorsqu'on en a besoin, le cerveau est soulagé et on passe moins de temps à réfléchir car le module fait tout pour nous, tous les utilisateurs de Firefox devrai l'utiliser

SUPER