Prayer: Is correct Arabic pronunciation necessary for the validity of obligatory prayers?

Practical Laws of Islam as per the teachings of Imam Khamenei

Prayer: Is correct Arabic pronunciation necessary for the validity of obligatory prayers?

English:

Question #465:

In obligatory prayers, is it necessary to pronounce all the words properly? Can a prayer be considered correct when the words are not pronounced correctly in the Arabic language?

Answer #465:

It is necessary to pronounce all the obligatory dhikrs of prayer including Al-Fātiḥah, the other chapter, and other parts correctly. If a praying person does not know the correct pronunciation in Arabic, it is obligatory for him to learn it. However, if he is unable to learn, he is excused and should recite them as he can and it is a mustaḥabb caution to offer the prayer in congregation.

-Imam Khamenei, Practical Laws of Islam, Importance and Conditions of Prayer