When you adress a reminder to the pseudouser "assignee" it is shown in german as "Bearbeiter", which is correct.
But when you adress to pseudouser "watchers" it is shown as "Beobachter verwalten", which means "Manage Watchers".
Similarly, when you adress to pseudouser "voters" it is shown as "Wähler anzeigen", which means "Show Voters".
I think you grab the wrong i18n-Key, so you get the wrong display-value.
On the other hand, it might be not your fault at all, but a jira-i18n-Bug. That used to be quite common, historically.