When installing windows with default language not set to english and changing it after installation you will notice that on the login screen the language is set to the language selected during installation. To change it english you need to edit the registry key HKEY_USERS\.DEFAULT\Keyboard Layout\Preload. In this key you will find probably 2 values named 1 and 2. You need to switch between the values so that the value named 1 will be set to 00000409 which is english. It happens to me when I get a new computer that is from a specific vendor and the OS is already installed.