There is a keyboard shortcut that you can press and that will change the keyboard language if you have multiple keyboard languages enabled in Windows system. This happens usually when you press left Alt + Shift together.
To disable that please press these keys in Windows and turn the multiple language option off and that should prevent this from happening in game, should you press these keys together.
For Windows 7:
Was Swedish layout I wanted to use, but ofc same methot to fix. Just go into Control Panel - Region and Language - Keyboards and Languages tab. Click "Change keyboards"... button.
In that window remove English (select, and remove button on right hand side), leaving only your wanted language. In case of more than one option per language (i.e. "Ink Correction (64bit Only)") in both or all languages, just remove it from the English side, unless you know exactly what it is and don't need it for either language.
Anyhow, when you have cleared any "unwanted" options in there, just apply and play on.