I've been reading the book, "Diary of a Wimpy Kid," for years. I've been reading the book, "Diary of a Wimpy Kid," for years.

I've been reading the bookAmerican book series "Diary of a Wimpy Kid" for years. I've been reading the American book series "Diary of a Wimpy Kid" for years.

注：1冊の本ではなく、19冊の本のコレクションらしい。従って、「book 」よりも 「book series 」の方が良い。NOTE: It seems is not a single book, but a collection of 19 books. Hence, "book series" is better than "book."

I've been reading the bookseries, "Diary of a Wimpy Kid", for years. I've been reading the series, "Diary of a Wimpy Kid", for years.

I always find ait difficulty of to reading it because I find four or five phrases that I don't know on almost every page. I always find it difficult to read it because I find four or five phrases that I don't know on almost every page.

I always find aより自然に： It has been difficulty of to reading it because I findthere are four or five phrases that I don't knowunknown phrases on almost every page. より自然に： It has been difficult to read because there are four or five unknown phrases on almost every page.

I've always fiound ait difficulty of to reading it because I'll find four or five phrases that I don't know on almost every page. I've always found it difficult to read because I'll find four or five phrases that I don't know on almost every page.

I always find ait difficulty tof reading it because I findthere are four or five phrases that I don't know almost every page. I always find it difficulty to read it because there are four or five phrases that I don't know almost every page.

I always find ait difficulty of to reading it because I findthere are four or five phrases that I don't know on almost every page. I always find it difficult to read because there are four or five phrases that I don't know on almost every page.

Whenever I come across new phrases I have to look ithem up. Whenever I come across new phrases I have to look them up.

Whenever I come across new phrases, I have a tendency to look ithem up. Whenever I come across new phrases, I have a tendency to look them up.

LOGIC: Some readers might guess the context without using a dictionary to read. (Different readers have different reading styles.)

Whenever I come across new phrases, I have to look ithem up. Whenever I come across new phrases, I have to look them up.

Whenever I come across new phrases, I have to look it up. Whenever I come across new phrases, I have to look it up.

Whenever I come across new phrases, I have to look ithem up. Whenever I come across new phrases, I have to look them up.

ALSO POSSIBLE: That was quite a fewn achievement for me. ALSO POSSIBLE: That was quite an achievement for me.

That was quite a few pages for me. That was quite a few pages for me.

MY GUESS: I had never read that many pages in a foreign language. MY GUESS: I had never read that many pages in a foreign language.

私の推測では、あなたは母国語でそれ以上のものを読んでいる。My guess is that you have read more than that in your native tongue.

Actually,This time I didn't look up any new phrases. This time I didn't look up any new phrases.

"Actually" wouldn't be used here! The sentence makes sense without that word as well, but you can add something like "This time" to explain it better

ActualSurprisingly, I didn't look up any new phrases. Surprisingly, I didn't look up any new phrases.

I just guessed their meanings through context. I just guessed their meanings through context.

I still have a quarter of one book left, but I just know I can finish reading it within this year. I still have a quarter of one book left, but I just know I can finish reading it within this year.

I still have a quarter left, but I just know'm certain that I can finish reading it withinby the end of this year. I still have a quarter left, but I'm certain that I can finish reading it by the end of this year.

I still have a quarter left, but I just knowfeel like I can finish reading it within this year. I still have a quarter left, but I feel like I can finish reading it within this year.

Your grammar was correct but I feel like this is a bit closer to your native text

I still have a quarter of the book left, but I just knowthink I can finish reading it withinby the end of this year. I still have a quarter of the book left, but I think I can finish reading it by the end of this year.