Hi I run into this bad edit made with 2017 wikitext editor by User:Omotecho. The template c:Template:Contact author before editing/lang asks people to recreate the template by "replacing the whole page with: {{subst:lle}}". Unfortunately with this editor, wrapped the template in <code><nowiki>.
Topic on Talk:2017 wikitext editor/Flow
The user probably copy pasted it, and then the editor asks the user to convert the html to wikitext or not. If you don't know wikicode as a user, it isn't easy to know what the right answer is, and what the result of that answer is, and how to adapt that. If you convert the html to wikicode, you will get something like this bad edit. The right choice is NOT to convert (keep the literal text, ignore the html markup).