When I pray at the masjid, the assistant imam makes mistakes in his recitation so often that no one bothers to correct him anymore. how does this affect the prayer of the congregation?
You must not pray behind a person if he does not recite correctly, however you are not responsible for the rest of the congregants, for their prayer is considered valid if they do not realize the mistakes. Moreover, you should kindly advise the Imam of his reciting errors if possible and if it doesn’t hurt.