Is congregational prayer valid if led by a non-Arab whose pronunciation of some letters is unclear, while there are two Arab worshippers, one of whom shaves his beard and the other is a smoker?

If the Imam does not mispronounce Al-Fatiha in a way that alters its meaning, then it is permissible to pray behind him, and he should be given precedence over others due to his commitment to religious principles. Sheikh Al-Islam Ibn Taymiyyah stated that a pious believer is more deserving of leading the prayer than a fasiq (transgressor), even if the fasiq is a better reciter or more knowledgeable, because praying behind a fasiq is prohibited. It is not permissible to appoint a fasiq if it is possible to appoint a righteous person.