Language is not saved.

Good day
I have a problem and can not find a solution:
I installed the plug-in, configured it and it works well, but when I go to another page, the language I selected disappears and I have to choose the one with the page reloaded
How it is possible to make so that the prefix ру / ен / (for example) remained? The language is not saved when switching to another page, and this is bad