So I watch a lot of anime series and I thought it would be good to turn my hobby into something useful, and it seemed a good idea to start learning Japanese.

It's a long sentence, a comma somewhere makes it nicer.

I did some research and I found out that the Japanese language has three alphabets – hiragana, katakana and kanji.

Hiragana and katakana have 46 symbols each, and kanji over 50 ,000, and each symbol means a whole word.

More commas :) It looks very "foreign" to write numbers like that in English.

To be completely proper it should probably be "and kanji has over 50,000", but your wording is quite natural to me.

At first I thought that hiragana and katakana iswere some kind of easier alphabets for those don`'t know or don`'t want to learn kanji.

Plural, so "were". Using ` as an apostrophe is easily understandable but looks very strange. If you can easily use ' you should.

Japanese uses all three alphabets at once and you should know at least 2000 kanji symbols to be able to read a simple article.

Or "Japanese people use" or "The Japanese use".

So I understood that for me Japanese is impossible to learn and it is a very stupid idea to learn it because I like anime :D So that was my fifteen minutes of learning Japanese :D

Slightly awkward, but okay. Would be a little clearer as "Japanese is impossible to learn and trying to learn it because I like anime [is/was/would be] a very stupid idea"