You are mixing two things. Learning a language and learning a codebase. Those are not the same thing. Besides, you are also just talking about what happens du

You are mixing two things. Learning a language and learning a codebase. Those are not the same thing. Besides, you are also just talking about what happens during the first N months. Most companies I've worked for allow for time to learn the language(s) being used. Some of them will fire you if you can't show sufficient progress over time.