Ctrl key inverts the pressed letter instead of invoking the shortcut command

I have a Dell Precision 3581 and an external keyboard Logitech K850. The problem is that, on both the keyboard of the laptop and on the external one, when I click Ctrl + a..z I just get the secondary language letter instead of running the command. So, for example, when I want to make a command search with Ctrl + r, I get the Cyrillic р instead of a prompt to write a search phrase. Does anybody knows what can be the problem here?

Question by malkoto1 on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.