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.
The Fatwa that we adopt here in Islamweb is that it is permissible for a praying person to exalt the mention of the Prophet during prostration in obligatory prayers, because the prostration is one of the situations in which one should supplicate and one’s supplication may be answered as the Prophet said: "…and while prostrating yourselves be earnest in supplication, for it is most likely that your supplication will be answered.” [Muslim]
Moreover, exalting the mention of the Prophet and sending prayers upon him is included in the general meaning of supplication, so we think that this is permissible. However, it should be noted that exalting the mention of the Prophet in the prostration does not mean that by doing so we are not required to exalt his mention in the Tashahhud in the last Rak’ah of the prayer.
As regards supplicating in a language other than Arabic, then it is permissible for a person who does not speak Arabic to supplicate Allaah in his language; for more benefit, please refer to Fatwa 90022.
Allaah Knows best.