Similar to what the user with fancy letter said, you have to immerse yourself somehow, whether it's travelling to a place where it's regularly spoken and make an effort to speak it, or reading that language books along with a translation until your start recognizing patterns. If you are using a show or other material, you have to ask yourself to try to respond to questions in that language, or make questions that you would ask the show members or writer, etc. like:

De qu'est-ce qu'ils parlent?

Qu'est-ce qui se passe en la dernière partie?

Comment répondrais-je a ce question?

Quel est la message l'auteur (ou le personnage) envoye a moi?

The idea is passive listening will help you kind of understand what people are saying but it will still be difficult to make your own sentences. You have to learn it just like a little kid does.

I comment on jlai.lu and some of the Québecois communities occasionally but I often have to use translate to double check my work, because I'm like shit what was this word again or which grammar form was it? My high school French education was enough to stumble through ordering train tickets in Paris. I have no formal German education but I can grasp simple stuff posted to feddit.de German threads and I'm trying to get better.

I just need to spend a lot more time learning it and likewise you will need to follow up the time you spend passive listening to the French sitcoms with active learning and trying to figure out the language, so you should have additional resources ready to help with that.

ETA: Some of the resources other users suggested like Language Transfer seem interesting, I'll give it a try myself too!