Which Unicode characters are "safe" in Glulx?

You just marked my previous answer as the solution… but I wouldn’t say the same thing now that I did 2 years ago.

As of the latest release, 2023.1 Gargoyle now bundles unifont. So far as I know, that was the only major interpreter app that wouldn’t automatically draw upon system fonts.

It may be the case now that about the only people left who would be expected to have troubles with Unicode symbols are people deliberately running a minimal Linux and they know how to install a font if they want to. So… I finally think it’d be pretty reasonable to count on being able to use the Basic Multilingual Plane.

Of related interest, the (unscheduled) next release of Inform will be able to handle Unicode input (on glulx) and won’t impose an artificial limit on what characters can be output or used in texts.