To switch between two language, proe needed to be restarted each time.
method 1) You can modify the start-up setting, but you should remove any "environment variable" like 'lang'=german. In the proe installation folder, somewhere in C:\Program Files\proeWildfire 3.0\bin\.....you can find "proe1.psf", it is a start-up setting and open by notepad. To have the german start-up, add "ENV=LANG=GERMAN" at the last of all settings.
If you want to have a selection box, copy proe1.psf to proe2.psf, eg
in "proe1.psf"
modify "DESC=English"
add ENV=LANG=ENG
in "proe2.psf",
modify "DESC=German"
add ENV=LANG=GERMAN
then you have this.
You can also create proe3.psf to have another language.
Method 2) Use "environment variable" settings, set pro_lang=german. But you need to remove the start-up settings as above, remove the last line ENV=LANG=ENG or ENV=LANG=GERMAN. The environment variable will override the language start-up setting. You need to set pro_lang for each language switch.
Whatever method 1) or 2), in config.pro, dialog_translation, help_translation, menu_translation, msg_translation set to yes. Otherwise, proe default show English.