There is reward in praying the translation of the Quran but not the same as actually reciting the quran. The Quran was revealed in the Arabic language and anything else is a translation and not the Quran Al Karim. There is immence reward in reciting the Quran whether one understand it or not.
Abdullah Ibn Masud (Radi Allahu Anho) Narrates that the Messenger of Allah said “Whoever recites one letter of the book of Allah has one reward, and rewards are multiplied by ten. I do not say that Alif Laam Meem is a single letter, rather Alif is a letter, Laam is a letter Meem is a letter (i.e. thirty rewards) (Tirmidhi)
Allah has chosen the Arabic language and it is the language of His beloved Rasool. English cannot compensate for the beauty of the Arabic language. Arabic will be the language of the people of paradise.
Reciting just the translation in the Salaah would make the Sallah invalid.
If your mind starts to wander then leave the recitation. One should read the Quran with the respect and attention it deserves. If by reading only a few Rukoos or verses the mind is fully attentative and after that it wanders then read only a small amount. The Prophet of Allah said that do things regularly even in small quantities.
[Answer provided by: Muhammad Salim Ghisa]