The edit page text editor wikEd has a wikicode syntax highlighting function, that does "[h]ighlighting of different types of dash and blank characters". This function marks Em dashes (U+2014), En dashes (U+2013), Thin Spaces (U+2009), En Spaces (U+2002), Em Spaces (U+2003) and Ideographic Spaces (U+3000). It would be helpful to have a similar feature in the Extension:CodeMirror.
Topic on Extension talk:CodeMirror
That's a good idea, @X black X. I created task T196934 to keep track of it. I wouldn't promise that we'll work on it soon because we have the whole new wishlist to go through but we'd definitely try and come back to it when we get the time to.