How to debug wrong passphrase (may be wrong encoding?)

I am using GPG with PGP/MIME on The Bat! 11.0.
In a test for a german user i found this:
Encryption+Sign works when we do not use local german characters for passphrase.
Means passphrase test works.
When change passphrase to äöü Encryption+Sign fails.

Passphrase was added for PGP key in Kleopatra.

How to debug this?
Which gpg.conf and gpg-agent.conf is needed?

Issue resolved now by Ritlabs bug fix in The Bat!

//EDIT: But question still valid, how to debug password sending by command line from an other program can be debugged.