Why do most new languages fail? (2012)

This 13-year-old article lists problems after a language has been implemented. Well before that happens, a big red flag would be the creator created the language more for the challenge of designing and implementing a language, rather than filling some real need for a new language. Also, even if a language doesn't have the flaws the article lists, a decent language is still doomed if it doesn't have the necessary critical mass of actual users.

To quote an AI lookup: Sources like The Historical Encyclopedia of Programming Languages list thousands, with some estimates reaching close to 9,000. The TIOBE Programming Community Index tracks over 100 actively used languages based on popularity.

That's a lot of competition.