At the Bodleian we have added a facet to be able filter resources and archival objects by their language of materials:
Scroll down and look on the left. The same language facet is also in our staff interface.
Would this be of use to other ArchivesSpace users?
Looks good to me on the public side and on the internal side as an Admin/Advanced/Archivist. Language of materials is visible as a facet/filter for objects.
This is working well.