Arne's description was correct except for the folder name. The files should be just in the $PHEX/lang folder.
I repeat the steps in a short summary again:
- Create a file $PHEX/lang/language.list and add a single line nl_NL
This file is used to build the language list in the UI. - Create a file $PHEX/lang/Lang_nl_NL.properties or $PHEX/lang/Lang_nl.properties and translate the text in it.
- The order Phex uses to search for translations is nl_NL, then nl and then it will fallback to use the default english language file. The first found translation will be used.
Gregor