The territory names are hierarchical as in country or country-territory to allow overriding higher level values (for example in the US Virgin Islands there is left hand traffic, so that requires an entry for us-vi). Note the lower level entries do not inherit properties from higher level ones.
Currently the data is not versioned, to contribute please create a pull request.
Properties:
"distance" unit system for distance and speed "metric" (default) or "imperial"
"left-hand-traffic" side of the road that is driven on, false (default) or true
"speed-limits" array of common speed limits in the territory, if "distance" is "imperial", the units are assumed to be miles per hour, otherwise km per hour
"languages" array of language codes for the territory
"address-keys" array of OSM tag keys used in addresses in the territory
Ideas for additional properties
"vienna-convention" signatory of https://en.wikipedia.org/wiki/Vienna_Convention_on_Road_Signs_and_Signals
"phone_number_format"