Just use lat/long which are universal.

I'm no supporter of plus codes or w3w, lat/long are no panacea. In particular, (a) they're quite long, which is inconvenient for writing on envelopes or entering into sat nav systems; (b) there's no way to detect swapped or miskeyed digits, which depending on the digit can cause arbitrarily large errors; and (c) they're difficult for humans to parse compared to city and country names.