Whilst I could see this as useful to some, I feel that this is taking Joplin more towards being a word-processor rather than a notes app. I just wonder if this sort of facility is necessary for this type of application.
If I were to need such characters I would just use Alt+ codes such as:
and I feel that smart-quotes are also more of a word-processing / DTP sort of thing.
I rarely need them in notes and if I do it tends to be the fractions. If the contents of any of my notes were later to be used in a more formal document and did need any of these I would use a word processor.
Please do not think I am having a rant , I am just throwing my particular view into the thread.
I’d accept a PR and as far as I know it’s an option of the Markdown renderer. In our case, we should make it look like a plugin though, like we did for the soft break option.
Maybe it's simpler on Windows, since Windows is still stuck in the stone age with its Alt+codes. Compose key works much easier (and there are thingies for Windows as well) but, and that is most important, it works identically in all applications. Having one application behave differently from another because both have their own (but different) support for 'rare characters' quickly becomes a PITA.