I cannot say I have had the experience you describe. Most repos describe their stack clearly, or you can figure it out easily enough. Is it really a common problem for you?
Do you mean in the project readme description? I'm talking about programming languages that are returned by the github API for a specific repo.
For example in my portfolio site I had to show the technologies used in my projects but for a nextjs project the github API returned only typescript and css while I used react, tailwind, ...