Thanks @Robert Barbiaux, that's really helpful.

If only MSH-18 were set... 🙄 Up-stream system isn't setting it! And until yesterday supplier of upstream system was claiming they were sending UTF-8 when we thought the feed looked awfully like Windows-1252. Yesterday they admitted/confirmed they are sending Windows-1252, so at least now we know!!

We've got the same issue, but with an incoming HL7 feed with embedded, encoded characters - would be nice to be able to detect what's coming in, but I take it from this discussion that's not (reliably) possible. Don't really want to scan the whole text of every incoming message to heuristically look for possible encodings. Upstream say/think they are sending UTF-8, but we seem to be getting Window-1252, for the characters we've seen in the (limited) testing. Who knows what will come through the feed once it goes live!