You can check your language/keyboard on the bottom right of the screen:
What keyboard do you have? (The exact model/name so that i can check it out.)
Did it stop working immediately after switching the keyboard?
Also try to enable/disable V-Sync. I remember that it had problems with keyboard and mouse input in a few special cases back then in the alpha (Key presses sometimes missing, etc...).
I'll look into the alpha v5 code again to see if there is something that i might have missed.