I don't know if I should report this here or somewhere else, but anyway there is a typo on https://translatewiki.net/wiki/MediaWiki:Wiki-seo-pageinfo-below/en which points to https://'mediaiwki.org/wiki/Extension:WikiSEO instead of https://'mediawiki.org/wiki/Extension:WikiSEO . Now, I've changed all the links on the relatively few translations that were at the time of writing and the message documentation but more could crop up with the same error.
Topic on Extension talk:WikiSEO
Good catch and great effort. This translation source must indeed be changed in the code repository of this extension to prevent this typo from propagating.
Thanks for the report! The URL is fixed in the latest commit.