A lot of siteinfo interwikimap url does not exists but is redirected to https://wikisource.org/wiki/Main_Page
Sample:
https://wikisource.org/w/api.php?action=query&meta=siteinfo&siprop=interwikimap
{ "prefix": "ie", "local": "", "language": "Interlingue", "url": "https://ie.wikisource.org/wiki/$1" }, { "prefix": "ig", "local": "", "language": "Igbo", "url": "https://ig.wikisource.org/wiki/$1" }, { "prefix": "ii", "local": "", "language": "\ua187\ua259", "url": "https://ii.wikisource.org/wiki/$1" }, { "prefix": "ik", "local": "", "language": "I\u00f1upiak", "url": "https://ik.wikisource.org/wiki/$1" },
Please provide an additional key like redir_url to give an hint that the given url has no distinct site from mul.wkisource.org but is redirected to that.