How to set default language for eclipse or for your RCP product

Before you launch an eclipse, configure  -Duser.language=en property in eclipse.ini file.

In the context of mac os.

Example:

1. Go to /Applications/Eclipse/eclipse.app/Contents/MacOS/
2. Open eclispe.ini file
3. Append -Duser.language=en to the end of the file
4. Restart eclipse

In windows, you can find eclipse.ini file in the eclipse root directory.