I think there's a serious bug for all who don't use MC12 in english.
It looks like you've done a good job with your translations - but maybe you translate a bit too much.
For example, when running MC in german, the field [Artist] is named [Interpret]. This also applies for rules. I use the "Rename files from properties" function to place my files according to their nature. E.g. albums, chart tracks, etc. are arranged via rules.
For the filename I use the following rule:
If(ISEQUAL([Album]),Unknown Album),[Artist] - [Name],[Track #] - [Artist] - [Name])
When running this in german this is changed to:
If(ISEQUAL([Album],Unknown Album),[Interpret] - [Name],[Track #] - [Interpret] - [Name])
The field [Interpret] is not recognized - surprisingly the field [Titel-Nr.] is!
The result of that expression is:
01 - [Interpet] - Feel so real.mp3
Another issue in that example is that the expression itself doesn't work anymore. If I want to ask if an album field is empty the expression above was the one that worked. How is this working today?