Good work. Well, I'm French so I can understand how learning English can be frustrating sometimes. But to be fair there are some similarities between French and English. As for me, I managed to progress through listening podcasts and watching movies, TV shows or just YouTube videos in English on a regular basis. I used the subtitles at first, then I progressively realized that I didn’t need them anymore, except in a few particular cases. It’s a good way to study English without necessarily having the feeling of working hard or exhausting yourself. Also, I worked as a scientist before and as you rightfully mentioned, English is an official language, almost all of the scientific literature is in English, so I suppose that also helped a lot in my case. Sorry my comment is a bit dense. If you have any questions feel free to send me a message.