Hello, I just registered and I want to improve my English. Hello, I just registered and I want to improve my English.

Hello, I just registered and I want to improve my English. Hello, I just registered and I want to improve my English.

Hello, I just registered and I want to improve my English. Hello, I just registered and I want to improve my English.

'Register' should be in the past tense, as it is a completed action

Hello, I just registered and I want to improve my English. Hello, I just registered and I want to improve my English.

Grammar: “I just register” → should be “I just registered.”

I'm not sure about my level,; I suppose it's around B1. I'm not sure about my level; I suppose it's around B1.

I'm Frencha native userspeaker of French. I'm a native speaker of French.

I'm Frencha native usFrench speaker. I'm a native French speaker.

I'm not exactly sure if this is exactly what you meant to say.

I'm a French native user. I'm a French native user.

Need to use 'a' - could also say "I'm a native French speaker" or "I'm a native user of French" or "I'm a native speaker of French" - I'm not sure that we 'use' language (in English)

I'm Frencha native usFrench speaker. I'm a native French speaker.

Word choice: “French native user” → more natural is “I’m a native French speaker.”

I read some of your historiejournals before sendwriting mine. I read some of your journals before writing mine.

I read some of your histories before sending mine. I read some of your stories before sending mine.

I read some of your histories before sending mine. I read some of your stories before sending mine.

I think you might mean 'stories' or 'posts' - histories in French would be (I think! I used Google Translate) the same as "histoires"

I read some of your histories before sending mine. I read some of your stories before sending mine.

It' was quite fun. It was quite fun.

Or you could also say "they were quite fun," if you meant the stories themselves rather than the experience.

I'll like to be level C2 next week but I know it's a sweet dreamunrealistic. I'll like to be level C2 next week but I know it's unrealistic.

This isn't a natural expression. You could just say that's it's "unrealistic" or "impossible"--or, if you want to say that something you desire is both unrealistic and maybe even a little crazy, you can say it's "a pipe dream."

I'll like to be level C2 next week but I know it's a sweet dreamlong shot. I'll like to be level C2 next week but I know it's a long shot.

colloquialism - "long shot" is something that might be impossible to achieve

I'll would like to be level C2 next week but I know it's a sweet dream. I would like to be level C2 next week but I know it's a sweet dream.

Sentence structure: “I’ll like to be level C2 next week” → better: “I would like to reach C2 level…”