Here is how we use the passphrase error codes:

11 = (0, 11) = (GPG_ERR_SOURCE_UNKNOWN, GPG_ERR_BAD_PASSPHRASE) = (Unspecified source, Bad passphrase)

    GNUPG: - The entered passphrase does not verify

31 = (0, 31) = (GPG_ERR_SOURCE_UNKNOWN, GPG_ERR_INV_PASSPHRASE) = (Unspecified source, Invalid passphrase)

    GNUPG:  - Required constraints of the passphrase are not met.

What is wrong with "bad" - In German we translate it to "Falsches Passwort" in Danish to "Ødelagt adgangsfrase"

Both in Kleopatra and in Okular the BAD_PASSPHRASE gets converted to "Wrong passphrase" rather than just using the error string from gpg(me).

Also; The Danish translation is closer to "destroyed passphrase"

In T8338#221699, @werner wrote:

We also have BAD Signature - thus BAD Passphrase can't be that wrong. Iw ould hesitate to change this after 28 years.

Why and how doe Kleo use a differet translation here. The rule is to use the gpg_strerror(err) output?

I don't know. @ebo asked me to change it in Okular (because Kleo does it)

BTW, can you please provide a better Danish translation which is more alingned to the German one?

The danish translation seems to really require some work. The GnuPG one is lots of fuzzyness and weirdness, and disagrees with the .po file in libgpg-error on some terms.
I'm also not sure I agree with the entire choice of archaic vocabulary used for the danish translation all over, but maybe I can do a minimal set of changes.

Also, what's the difference between "Invalid passphrase" and "bad passphrase" ?

In T8338#221702, @svuorela wrote:

Also, what's the difference between "Invalid passphrase" and "bad passphrase" ?

See T8338#220385 . One error occurs when a user is asked for a new passphrase. The other occurs when a user enters a wrong passphrase.