Hello Dear Diary, ¶
Today I made a to-do list which I want to complete before the end of this year.

And of course it has started with speaking english.

People say that you should practice reading, writing and speaking.

But I will forget everything and begin to my new life with my to-do list.

Hello Dear Diary, ¶
Today, I made a to-do list whichto complete before the end of this year.

"Dear" is used as a greeting so you'd have either "Hello diary" or "Dear diary" but it doesn't make sense to have both; it'd be like saying "Hello hello diary"

And , of course, it has starteds with speaking eEnglish.

So, I have 119 days left.

I don't have no idea how can I improve my eEnglish but I will try.

People say that you should reading, writinge and speaking.

But this situation is not as easy as they sayit seems, especially for me.

But I will forget everything and begin to my new life with my to-do list.

Hello Dear Diary, ¶
Today I made a to-do list whicof things that I hope to accomplish before the end of this year.

Just some minor touch-ups

And of course it has started with—with the first one being to practice speaking eEnglish.

I attempted to connect your two sentences to make them sound more natural

So—and I have but 119 days left.

I don't think that very many natives would speak like this, however the sentence is redeemable if you add a literary flourish.

I don't have idea how can I improve my eEnglish, but I will try.

As a proper noun, "English" should be capitalized. There also needs to be a comma to separate parts A and B of a contrasting sentence (A, but B)

People say that you shouldOthers usually recommend practicing reading, writing, and speaking. as though it is altogether simple

But this situation is not easy as they say especially for me—but while there is merit to what they say, I wonder if those reciting these rote statements truly understand how difficult this process truly is.

I would have personally deleted both this line and the last one, but I decided to preserve them to provide you with experience for how such a sentence could ~theoretically~ be made to work if one day you needed to use similar words in another situation.

If only I could describe how much hardship I'The difficulties that I have endured up to now. are indescribable,

Your sentence was grammatically correct, but felt somewhat disconnected from the rest of your post.

Buthowever I will forget everything and begin to my new lifeset aside the past and move onward toward the future, starting with my to-do list.

Just some more touch-ups