Rename files with non-utf8 characters using detox

I am trying to use detox in the following way detox -s utf_8-only -r -v -n to detect invalid filenames on my system. The command performs mostly ok. Unfortunately it falsely detects also German Umlauts (äöü etc.) which I would like to keep. Note that they are in utf-8 encoding. Can I alter the command such (e.g. by adding filters) that it will ignore filenames with Umlauts?