My language journey started as many others people's did - at school.

This is tricky because 'many other people' possess a journey. The long form would be:
"My language journey started as many other people's language journey did - at school."
An alternate way to express the same thing while avoiding the possessive is:
"I started my language journey like many other people - at school."

In the beginning e, English was a fun subject at which. I was able to get good grades, but as time went on grammar rules overwhelmed me. It got to the point that I started hating the language.

Aside from the minor spelling error, nothing is wrong with your version ..... if it were spoken. But when you write English, punctuation becomes very important. (Bet you really hate that!) A simple rule is that if you have a subject and a verb, it is a separate sentence.

Fortunately, it changed in the second year of high school when I gotith a new teacher.

Friends from other groups were telling me that she iwas very strict and expectsed a lot of work from students.

This is in the past, so all verbs should be in the past tense.
Stylistically, you can drop 'from other groups.' It isn't wrong, just seems irrelevant to the story you are telling.

I gotThis scared hearing thisme as I believed my level of eEnglish was terrible, but it also motivated me to work more than in previous years.

Students in America (not sure if it applies to other versions of English) would say "I'm terrible at math" or "I'm terrible at English." Perhaps because of the way we grade our subjects, American students don't usually think of their learning in terms of levels unless they are talking about applying to college.

Also, 'I got' is an all purpose phrase that is commonly used. However, it gets a bit boring when overused in writing.

It turned out that the teacher was strict but only when it came to vocabulary and s. She was neglecting grammar - which suited me wonderfully.

When I finished high school, I started watching TV series in eEnglish without subtitles which went surprisingly very well.

Again the corrections here really only apply to written English. If this sentence were spoken, there'd be nothing to correct.

At this point, after 12 years of learning eEnglish at school, I stopped actively learning itstudying the language because I was satisfied with my level in this languageunderstanding of it.

Commas set off phrases that add to or clarify other parts of the sentence. Often, can tell where the commas go when you hear a sentence spoken. If you hear a slight pause, that is where a comma goes.

'Study' has the same idea as 'actively learning' and is a bit simpler.

Though, as time went on, I gradually realised that my speaking and writing skills are much poorer than listening and writreading.

I made an assumption that you didn't mean to put 'writing' in both places.

An alternative ways to say this:
"Gradually, I realised that ...."
"Slowly, I came to realise that ..."

Because of this, I'm taking part in this challenge to find out my shortcomings and to, focus on improving my grammar, and to make my writing sound better.

Nice comma at the beginning of the sentence.

The commas I added are of a different sort. When writing, any list 3 or more phrases should be separated by commas. If you do this, you do not need more than one 'and to.'

This time, I'm prepared with knowledge about understand how important repetition is and I want to better plan my study.

Just a simpler way to say it.

My language journey started as many others people did - at school.

In this situation, others = people

In the beginning e, English was a fun subject at which I was able to get good grades but as time went on grammar rules overwhelmed me to the point thatwhere I started hating the language.

Fortunately, ithat changed in the second year of high school when I got a new teacher.

FMy friends from other groups were telling me that she is very strict and expects a lot of work from students.

I got scared hearing this asHearing this I was scared because I believed my level of eEnglish was terrible, but it also motivated me to work moreharder than in previous years.

It turned out that the teacher was strict but only when it came to vocabulary and she was. She neglectinged grammar - which suited me wonderfully.

When I finished high school I started watching TV series in eEnglish without subtitles which went surprisingly very well.

'very' not really needed

At this point, after 12 years of learning eEnglish at school I stopped actively learning it because I was satisfied with my level in this language.

Though as time went on I realised that my speaking and writing skills awere much poorer than my listening and writing.

Because of this, I'm taking part in this challenge to find out my shortcomings and to focus on improving my grammar and to makeso my writing will sound better.

This time, I'm prepared with knowledge about how important repetition is and I want to plan my studyies.

studies (plural)
like studying over a longer period of time