I think IETF BCP 47 is the way to go for this (and is rougly a superset of what you’re saying). They also define a “more/less specific” selationship between tags so you can ask for “en-CA” and have the system decide “en” is still appropriate.

These days I think OMEMO is a better choice than OTR, if your client supports it.

I don’t know what your exact criteria for “sportswatch” is, but I’ve been very happy with my Bangle.js 2: https://banglejs.com/