This task is to replace the "available-langs.properties" approach for identifying which i18n languages to omit from being loaded into the triplestore with a more robust approach.
- give all such non-language files a specific suffix forcing their inclusion regardless of language settings, or
- arrange rdf files into top-level directories by language, including one top-level directory that is always loaded.
This ticket must be completed before merging the `sprint-i18n` branches into the `master` branch.
See: GitHub thread: https://github.com/vivo-project/Vitro/pull/160#issuecomment-621380973