Books using localized subject terms do not appear in the Directory results when filtering by subject term in different language

[MichSpieler]

When a user filters the Directory for a subject term, the results only show books with this subject term in the same language. Books that use a localized version of the subject term do not appear.

Example: filtering the Directory for the subject "Health and safety in the workplace" won't show a book that has the subject term "Santé et sécurité au travail" in the book info. Accordingly, books with the subject "Health and safety in the workplace" in the book info won't show when filtering for "Santé et sécurité au travail".

Expected behaviour would be that all books of a specific Thema subject term would show using the filter, no matter which localization of the Thema term is used.