JDeveloper picks-up the default locale language from the OS.

To change this and force JDev to a specific language:

  1. Open JDEV_HOME/jdev/bin/jdev.conf
  2. Add the following lines for English:
    AddVMOption -Duser.language=en
    AddVMOption -Duser.country=US

This will show all warnings and message details in English.

 

credit: OraTransplant.nl