Dinner is ready when it is done. I'm sure there are others in English as well.

Yeah, a thing can be ready to be used/eaten/etc. What confuses me sometimes is, for example, a doctor writing some notes on their computer and then saying to me "now you are ready", meaning that we're done and I can go.

In that context, my response would be "ready for what?"

Dinner being ready, my car being ready (at a mechanic), things like that have proper context that being ready means being done.

I'm an English as single language pleb though