A URL with more than 1 colon like https://en.wikipedia.org/wiki/Template:Welcome:Foo gets split before the colon.

https://en.wikipedia.org/wiki/Template:Welcome works fine.

It would be nice if it was not necessary to URL-encode it for the link to be correct.

https://stackoverflow.com/questions/1737575/are-colons-allowed-in-urls says that colons are allowed inside URIs, unless it's in the first path segment of a relative-path reference.

See also https://stackoverflow.com/questions/2053132/is-a-colon-safe-for-friendly-url-use