I can’t see your fictional American thinking to trigger the bot - which means someone would have to reply to that person to request a bot conversion.

I think that they would, given enough community encouragement to do so; things like "OP, please add @!cookunitsbot to your post" go a long way. Roboragi in r/manga for example works well in this way.

Alternatively, if my "I think" above is wrong: then "requested" could also include "explicitly set up by the mods", not just "triggered by the user". For me it already solves the main issue, that is bots chasing you across communities to boss you around or vomit trivia.

Similarly, there’s a music IDing bot on reddit that responds to human-language questions like “whats the song” which is 100% ok with me (and the users have always been pleasantly surprised from what I’ve seen).

Frankly I think that having a standard way to request bots is better for everyone (including the bot developers) than having it reply human questions. Even then, as long as it doesn't do this thing outside of its own "turf" (music communities), it should be fine.