(At least) the beta visual editor (I haven't tried on any project where it is not beta) enforces capital interwiki, although the habit is to write them lowercase.
So it saves the page with [[W:Foo|Foo on Wikipedia]] instead of expected [[w:Foo|Foo on Wikipedia]] even though the user wrote the lowercase.
| Status | Subtype | Assigned | Task | ||
|---|---|---|---|---|---|
| Open | None | T322340 Support editing interwiki links within the visual editor | |||
| Open | None | T129745 VE/Parsoid should use lower-case interwikis in preference to upper-case ones, regardless of what the user/editing software inserts |
@Omegatron makes the same request at https://www.mediawiki.org/wiki/Topic:Vhafnwe4nz32nhid
Volunteer-me agrees with Danny_B and Omegatron, and would additionally like it to stop lower-casing links to Project: space.