I like your ideas, they are really interesting. However, to me, your writing is not persuasive at all. These are my ideas, let's give it a look!
First of all, being grammatically correct
.... It's a choppy sentence. You can write:
One of the main and maybe annoying cause of learning a new language is grammar.
Not only it is hard
Not only is it hard
i.e.
Don't use abbreviations in your essay: "i.e"
; i.e., grammatical phenomenon that exist in one language doesn't mean that it exist in another one
In my view, this sentence is not good at all; it is advisable to cut this sentence out.
Not to mention, the Syntax, this means how the words are arranged to create a well-formed sentence.
Learners also have difficulties in syntax when studying a foreign language.
You are better to care more about the first sentences in paras. They are too short and unable to express your ideas.