If you have version 5.3.0 of the XMLmind XML Editor, then you can download and install a German dictionary package.

To do so, download and install the package per your operating system:

Operating System Installer to download Size How to install
Windows XXEGermanSetup.exe 1MB Run the installer. It will do all that is needed.
Mac OS X XXEGerman.dmg 945KB Run the installer. It will do all that is needed.
Linux XXEGermanSetup.tar.gz 933KB
  1. Decompress and extract the installer in some directory.
  2. In a Terminal, do 
    sudo ./installxxefrench