On Mac OS X you can launch an app in terminal with other language. You pass the whole app path to the executable in the terminal and include an extra parameter called AppleLanguages.
For example in German:
/Applications/FileMaker\ Pro\ 17\ Advanced/FileMaker\ Pro\ Advanced.app/Contents/MacOS/FileMaker\ Pro
To know the language IDs that work, you can check in the resource folder of the app what languages are available.
For FileMaker 14, you find: de, en, es, fr, it, ja, ko, nl, pt, sv or zh-Hans.