Hello,
I have a web page in 3 languages. I created categories in every language. The problem arises when the user wants to write a new item from the frontend, because they see categories from all languages. It is a confusing and it happens that users chooses the category in the wrong language and does not appear in they language.
Do you have any idea how to solve this?
imgur.com/C5fpHH2

Sure,

Allow each user access only to her/ his language or make menu items (frontend editing) which only allow the addition of items to certain categories.

Thank you for your answer,
I tried to do it, how u wrote, but is not working.
Im not sure if I understand :)
1. Setting up a language for any user does not work and I can not imagine setting up a language for every user. And the other thing is that users choose a language of their own choosing.
2. In Menu(back end)- New Article(K2 Item), you can set "Category Pre-Selection", but it only means that it will appear as the first option in the selection. Please see the pictures
the second option would be better for me because, we are planning a lot of users...
imgur.com/a/nNaa8

Since each K2 Category belongs to a certain language, in the K2 Users' group you can limit the permission to that category or categories.
This will automatically limit the users to the correct categories.

Hi Kikor,
thank you. Now I understand what do you mean. But hovever this solution is not for me, because users from one group are from different countries (different languages). This can only be done by few users but not when they are thousands or more. The users register only in two possible groups, divided by other criteria such as language.
I'm using jomsocia and plug in: Jomsocial - K2 User Integration

This is done in a per-group basis, but you will still need to manually assign a user to a group.
If manual isn't an option then you need a custom (developed) plugin which does this for you.