Декларируем:
Public Const KLF_ACTIVATE = &H1
Public Const KLF_REORDER = &H8
Public Const KLF_SUBSTITUTE_OK = &H2
Public Const KLF_UNLOADPREVIOUS = &H4
Declare Function LoadKeyboardLayout Lib "user32" Alias "LoadKeyboardLayoutA" (ByVal pwszKLID As String, ByVal flags As Long) As Long
Обращение к функции:
Русская раскладка
LoadKeyboardLayout "00000419", KLF_ACTIVATE
Английская раскладка
LoadKeyboardLayout "00000409", KLF_ACTIVATE