At the moment an empty list is returned for the languages field in the responses for /items and /items/{itemId}.
Collect the languages metadata from the knowledge graph (one-to-many relationship; ?lr dcterms:language ?lang, where ?lang is a string literal with ISO 639-1 or ISO 639-3 code, e.g. "en", "de", etc.) and return them as proper language name ("English", "German", etc.).