I was somewhat puzzled by encountering few apps (GIMP and Inkscape for which I had recently posted link to excellent tutorial) that defaulted their interface to language of Windows installation and gave no option to change it.
It can be quite inconvenient because it is often easier to work with complex interface in original language rather than [lacking] translation.
I may be wrong but it seems that issue is common for software using GTK+ for interface. However it is probable for other software that picks language from Windows settings as well.
Common advice is changing preferred language in Windows or adding environment variables. Not only inconvenient but also affects all software so might create need to toggle back and forth.
Other way I like much more is creating simple command line script that will set preferred language and launch specific app with that setting.
Example for Inkscape:
set lang=en start inkscape.exe
Save as inkscape.cmd, copy to Inkscape folder and use for launching. Change language code and executable name as needed.
Start command is used so console window doesn't get stuck open waiting for Inkscape to close.
Relatively simple and per application way to change auto-detected interface language.
By the way do you always prefer apps in your native language or used to working with software in some other (possibly more popular) one?