<p>From my own "key logger like" process I figured out that another process Locale is wrong (i.e. by sniffing few keys, I figured out that the foreground process Locale should be something while it is set to another). What's the best way to do this?</p>

I'd use
setLocale
from within that process to change it, and notify the process about this with some form of IPC like:
signals
sockets
pipes
from the process who knows