When MediaWiki is installed with installation in Ripuarian (ksh) language, there are various raw HTML tags during the installation process, mainly used to specify the language of some English words, e.g. Liß Mesch! (<i lang="en">Read me</i>). They appears in the interface because MediaWiki escapes some messages to prevent (real) use of HTML tags.
It can by partly seen on the screenshot in T66229 (the copyright in the footer comes from the installation language, and there are <i lang="en"> tags). I also tested it, and the file includes/installation/i18n/ksh.json has many such tags.