Hi John,
While we aim to make AtoM fully multilingual, there are still many quirks and issues to be resolved and improved upon. One of these is culture fallback - when a term translation is unavailable, AtoM should fall back to displaying the original source string. This works in most view pages, but currently not in many of AtoM's selects, such as the autocomplete fields in edit pages.
I can't think of an easy setting or minor code change that can resolve this in the short-term. The easiest workaround will be to add English translations to these German terms, which can be done simply by navigating to the term view page, flipping the user interface to English, and entering edit mode - you should be able to add the English translation to the term that way.
Be aware that there are a couple known issues translating all the fields available in the terms module - we've resolved one issue for 2.7 and hope to address the other, depending on time and effort involved. See:
For now, translating the authorized form of name should not cause issues.
If the terms in question have been entered using English, but in the German data entry screen, then it's possible we could construct a SQL query that will change these terms source culture to English instead. I couldn't find a ready example of this (though I did find a previously shared way to
add translations for a taxonomy name), but I can follow up with our developers if this would be helpful.
Cheers,