How to change the keyboard input language from your application

Hot Virtual Keyboard shows the current input language.

Method 1

You can change the input language using the Windows message WM_INPUTLANGCHANGEREQUEST:

SendMessage(GetForegroundWindow, WM_INPUTLANGCHANGEREQUEST, 0, NewHKL);

Method 2

You can change the current system language using the /CHANGELANGUAGE command line parameter.
1. Start the program
2. Change the language with a command like this:

HVK.EXE /CHANGELANGUAGE 0409

Language Codes:
English (EN) - 0409
German (DE) - 0407
Spain (ES) - 040A
French (FR) - 040C
Russian (RU) - 0419
...
Here you can find all language codes: http://msdn2.microsoft.com/en-us/library/ms776294(VS.85).aspx