Let me take the example PHP, since you mentioned it and I don't know enough to have an opinion.
PHP is generally claimed to suck badly. But even I can see that the "haters" on HN generally don't know/discuss the existing PHP frameworks and methods.
If I would look at PHP to evaluate it for a project, I'd look at if it seems fun to use (really important!) -- and if it would be usable with good coding standards and modern frameworks.
The bad things people talk about PHP (bad cruft in naming of methods, kludgy parts) are not relevant if it takes a few hours/days to learn that -- and if a good coding standard can limit yourself to a subset of the language. You need to do that for all languages anyway. (See JavaScript.)
But: One big red flag would be if the language proponents are language war fanatics that vote down criticism of their language/framework while attacking all competition. You probably know which ones I talk about.