Online play is just around the corner; see this discussion.
The character maps are what the TADS 3 compiler uses to transform text written in any given encoding into UTF-8. All text strings in a T3 file are guaranteed to be UTF-8.
Your players will need an interpreter of some kind, which could mean an install (frob, gargoyle) or not. If you package the game as a Windows executable, it wraps it in an interpreter for you. This interpreter handles the job of displaying the UTF-8 text, and it’s not something you need to worry about as an author.