I don't know tbh. You can make two copies of essentially the same community around the same interests/subjects with different names, underscore or no underscore. I think "mechanically" solving a problem like that is not a great idea, and that defining if two community should be merge fall into the hands of admins and administrators, not developers. If you are a mod of a community, or admin of an instance, chances are you know that such "clones" exist, and you either think you should merge and do it, or think you have a valid reason to stay apart and are free to do so.

Absurd example, but there is a city named "Chicken" (It actually exist !) A community about cooking chicken : eatin_chicken A community about places to eat in the city of Chicken : eat_in_chicken

I'm not sure... I'm pretty sure sometimes and in some languages, separating two words can really change the meaning of a title, don't you think ?