Steps to replicate the issue:

• Go to a sandbox, on a wiki that capitalises initial letters, like Wikipedia.
• Create a link that begins with a long S. [[ſ]] or begins with ſ that links to a page (e.g. if there's a page with the pagename Star, [[ſtar]])

Background: https://en.wikipedia.org/wiki/Long_s -- in Unicode, it's the character U+017F.

What happens?:

• ſ is automatically capitalised within the internal link to S (i.e. the standard Latin capital S), in the same way that the lowercase s in [[star]] produces a link to Star, [[ſtar]] ALSO produces a link to Star.
• A red link is shown, BUT when clicked on, it functions as a blue link, so [[ſ]] takes you to S (e.g. https://en.wikipedia.org/wiki/S) , and [[ſtar]] takes you to Star (e.g. https://en.wikipedia.org/wiki/Star)

What should have happened instead?:

Two alternatives here:

1. The link should just have been blue(?)
2. An alternative way of looking at this is that ſ should not be automatically capitalised, but instead be permitted as an initial character. That would enable a redirect to be created at ſ that redirects to https://en.wikipedia.org/wiki/Long_s and that [[ſtar]] should make a red link because it does not comply with modern orthographic conventions. This is GIGO (garbage in-garbage out).

Of these, the alternative does seem to make more sense.

Does this affect any other characters?:

An open question.

• The two lowercase forms of Greek sigma seem to work OK: [[σ]] / [[ς]]
• ı (dotless I) is capitalised to I, so [[ındia]] blue-links to India