The MCS `/page/definitions` endpoint supports Wiktionary definition lookups from an ActionMode button within wiki pages in the Android app. It is only available for English because of the substantial amount of non-technical / coordination work that would be required to expand it to more languages; the work necessary to make this happen is not on the agenda for the foreseeable future. This state of affairs is justified by the notion that the endpoint is "experimental," but it hasn't been meaningfully updated since ~early 2016.
I am currently in the process of extracting MCS bits from PCS, and I believe we should consider deleting this endpoint. Before doing that, we need to evaluate whether the current in-app usage justifies the computing and engineering resources needed to maintain the endpoint in production.
@Dbrant Can you weigh in here with usage numbers and other thoughts?