Mass import: names of manually added metadata keys are not translated in record table

[solth]

Describe the bug When adding metadata using the "+" button in the mass import form, the internal IDs from the ruleset are displayed instead of the label corresponding to the language currently selected in the user interface.

To Reproduce Steps to reproduce the behavior:

1. Go to 'Mass import'
2. Add a metadata to the record table using the "+" button in the table header
3. Check the name of the new metadata in the table header
4. See error

Expected behavior The metadata label corresponding to the current language should be displayed in the record table header

Screenshots Adding metadata with German translation "Signatur":

Instead of translation the internal metadata ID "shelfmark" is displayed:

Release 3.7 and prior

Additional context

• #6186 deals with a similar issue for metadata parsed from uploaded CSV files but does not resolve this issue for manually added metadata
• see https://github.com/kitodo/kitodo-production/wiki/Massenimport for details on how to use the mass import feature in Kitodo.Production