I have physical games that are Japanese only regarding language support, if it’s a PS5 disc or Switch cartridge: the covers are of course written in Japanese & the region code for it is JPN (even if consoles are region free, why are language locks still a thing regarding the software as there’s no ENG?)
But, can you still trade them despite accepting this caveat: locked under a language barrier as the UI’s in game cannot be reverted to English. (Also, the classifications use CERO framework rather than ESRB). Like a CERO D (17才以上対象) is akin to a ESRB M17 & CERO C (15才以上対象) is similar to ESRB Teen.
On why only have one language, maybe size, licencing for a given translation having different rules than the rest, focus in a given market, position of the planets… Could be N reasons.
On if you can trade games, only vaguely familiar with Canadian and American laws, but afaik, nothing should be stopping you? Maybe aside from a game being explicitly forbidden (dunno if either have such a list), or if they break some broader law not necessarily related to games.
Also more broadly, among people with Japanese as a second language, native Japanese speakers living in the two countries, collectors, resellers and import sales, I’d say you have a non-zero chance of finding someone interested.
And about age-rating boards, I don’t think I’ve seen them have Executive/Legislative powers in either countries, only as a recommendation/guideline measure. May be good to confirm on that though.