I experience the below problem with several consecutive versions of your otherwise fine piece of work, can you try to resolve it, thanks?
Not being a native English speaker, I have two keyboard locales selected from the Windows configuration, no tweaks applied.
When opening a php/text file with characters in Chinese, Arabic or Hebrew via SFTP from a Debian 3.16.7 server with the internal Editor, at some point the keyboard locale freezes to my own (Bulgarian, if that matters). When I press Alt+Shift, the locale indication changes from BG to EN in my Windows taskbar, yet in the internal WinSCP editor I continue to produce Cyrillic letters when typing. Once frozen, my keyboard starts to type only in Cyrillic in all open WinSCP windows and Editor windows and the only solution is to close the whole application and start it again.