All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad 
is His slave and Messenger.
Supplications during the performance of the prayer, whether when bowing or prostrating, can either be authentic supplications that are reported from the Prophet or inauthentic supplications that have not been reported from the Prophet .
The most correct opinion is that it is permissible to say the authentic supplications in prayer in a language other than Arabic for whoever is unable to supplicate in Arabic. However, it is not permissible to do so for someone who is able to supplicate in Arabic. This is the view of the Shaafi’i and Hanbali schools.
Nonetheless, in order to be on the safe side, it is better to avoid saying inauthentic supplications in a language other than Arabic during the prayer.
Allaah Knows best.
