App Language Chooser
By CTM Development
Open the Mac App Store to buy and download apps.
App Language Chooser lets you run an application using the language of your choice, to display the user interface. It is useful as a developer tool for localizers, or when you do not want a specific application to use your preferred system language.
exactly what I needed
This app does exactly what it says. I use it for testing my localized apps and it works great.