First question. My mother language is not english. If i watch videos and buy books only in my language,can it be a problem for my chess growth?
Second question. Recently i got internet in my house.Online i play only on a chess site. I have on mobile phone(where forum does not exist) only app of this site. Is playing only on a site a good or a bad thing?
Third question. I play same openings and i never change them. Sometimes they are secundary openings.If i go on to play them can i get better in chess(even a little)?
Fourth question. I am buying chess books for many years.Sometimes i read them and they appear a bit old. Does it happen only to me?
1 It depends on your language. Besides English there are excellent books in Russian, German, ...
2 Playing on a site is playing and so it is good. Preferably play classical or rapid, no blitz or bullet.
3 Yes always playing the same openings is good. Changing openings is a waste of time and energy.
4 One must collect and read them. Especially if there are few books available in your language. Read them and re-read them.
Your English seems to be good enough, judging by your post. Chess books are not classical literature with eleborate expressions and sophisticated wordplay, you don't have to be a C2 level speaker to understand them. Just saying.
1) Tons of good books are translated to other languages; it should not be a big problem in near future. Later when you learn English better, you will use books in English, and so on.
2) Playing only on a site is not a great thing for an improvement. OTB experiences and lessons at the chessboard are one of the best improvement methods.
3) It is fine to have a narrow repertoire, and even if your openings are not 100 per cent sound, opponents under 2200 OTB will hardly take advantage of it.
4) What do you mean by books "appearing a bit old"?
I mean that some lines are old or not exact. An example is enciclopedy of batsford of many years ago: it shows some lines that nowadays are dubious or wrong due to a new move found out in more recent time. You study variation but then you find out that white is not slightly better but it is slightly worse.
You can learn something from every book, and theory should not be the main focus point. I hope my input was useful.
1st Looks like your language might be Italian. Plenty of fine books in all romance languages. Easy to read foreign language chess books with a limited vocabulary.
2nd I think you should find some place or people to play over the board in person, just for the variety. But nothing wrong with online play.
3rd Individual choice. I never liked having a narrow repertoire. I want a taste of every opening that exists. I like the Spassky idea, serve from either side, be universal. But if you want to be super-competitive and your rating is important to you, narrow is probably better.
4th I have lots of books, some 30 -40 years old. There are still things to be learned from them. I go back through them often. The knowledge doesn't get wrong. It's just that new things may be discovered. But you don't want to be picking opening moves from a book anyway. The book presents, you evaluate, and make your own choice.
#5 Opening books are obsolete when they are printed. Opeining books often are plain wrong: recommend bad moves, miss important lines. Nobody knows anythinh for sure about openings. Do not study openings, it is a bottomless time and energy sink.
Here are some books in Italian langiage
Don't learn openings until around 2000 level. Learn opening principles instead