I would like to ask about prayer.
Is it permitted in Islam to take someone who does not master the reading of Quran to be an "imam", even if he knows the Quran by heart, he doesn't read the Quran in the right way which lead to the modification of the meaning I am asking you this question because in some mosques there are some imams who do not master the reading of Quran and when you say something to them they refuse to accept this and they persist in their faults, most of them are old people, What should we do as Muslims, prevent them from putting themselves as imams or we let them do that, bearing in mind that we do not know if our prayer is accepted or not? Enlighten us.

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

It is not permissible for you to pray behind someone who makes grammatical mistakes in a way that changes the meaning of Al-Fatihah, and your prayer behind him is totally invalid. You have to appoint another Imam if possible.

Imam al-Nawawi said: "If a person makes mistakes in other than Al-Fatihah then his prayer is valid and the prayer of the people praying behind him is valid. Because not reciting a Surah after Al-Fatihah does not make a prayer invalid, therefore there is no harm to follow him.

Ibn-Qudama, may Allah have mercy on him, said: "if the Imam changes the meaning in other than Al-Fatihah, this does not make the prayer void, and there is no harm for the people to follow him, however if he does it on purpose, then his prayer is not valid and consequently the prayer of the people praying behind him is invalid.

The solution to your problem is that a group among you should get together and explain to the imam that there are some conditions that any Imam should meet in order to lead the people in prayer.

Among these conditions is to learn the correct pronunciation. If he does not take heed and you are unable to remove him from the position of Imam, then do not pray behind him and advise him, and inform all the people about the reality of his condition in order to remove him form the position of imam or not to pray behind him. This is of course if he makes aberrant mistakes. However, if he does not make mistakes that change the meanings but he has only some shortcoming in recitations like the weakness in the correct pronunciation of letters but does not affect the meaning, then the prayer behind him is valid, but it is more appropriate to appoint another Imam.

Allah knows best.