Is a silent prayer behind an imam whose recitation of Al-Fatiha is suspected to be erroneous due to him being non-Arab valid, and is it obligatory to re-perform previous prayers if his error, which invalidates the prayer, becomes apparent later?

The prevalent view is that whoever takes the position of Imam is qualified for it and does not commit a linguistic error (laḥn) that invalidates the prayer. Therefore, praying behind such a person should not be prevented merely due to suspicion about his condition. If it later becomes apparent that he commits a laḥn that invalidates the prayer, then it is not permissible to follow him. As for the previous prayers that were performed behind him, they are not invalidated as long as his condition was unknown. The prayer of the congregants is valid if they were unaware of the invalidity of their Imam's prayer.