Thank you very much for your question. It is our pleasure to answer it.

In the name of Allah, We praise Him, seek His help and ask for His forgiveness. Whoever Allah guides none can misguide, and whoever He allows to fall astray, none can guide them aright.

New Muslims are required to learn enough of the Arabic language for what they need in Prayer in order for their Prayer to be accepted. It is known that whoever does not recite Al-Fatiha (the Oprning Chapter in the Qur'an) in Salah, his Salah is invalid, and Al-Fatiha is from the Qur’an. Having said that, the translation of the meaning of the Qur’an is not Qur’an, because Qur’an is only the Arabic words that have been revealed to the Prophet (peace be upon him). Until you know how, you may say dhikr (al-hamdu Lillaah (praise be to Allah), and La ilaaha ill-Allah (there is no god but Allah), and Allahu akbar (Allah is Most Great).

Takbeer (saying Allahu-Akbar in the beginning) and Tasleem (saying Assalamu alaikum at the end) must also be recited in Arabic according to the vast majority, if some one is completely incapable, and then they may say it in a different language.

Regarding the routine mention of Allah (dhikr) in the prayer (which you say in prostration, sitting and bowing etc) aside from the Quran and takbeer there is more controversy; however it is very important that you learn as much as you can in Arabic to perfect your prayer, since that is the most important deed in Islam after the pronouncement of shahadah. 

The fact that we all pray in the same language is unifying. Salat is our most important deed and we are blessed, as Muslims, to be able to pray together. Wherever you go in the Muslim world or outside of it, you can walk into any masjid and pray with them and understand part of what they said. At least the Fatihah is known bt almost all Muslims. This also protects our masjids from needing to be divided along ethnic lines in multicultural and linguistic Muslim communities, such as the Muslim minorities in the west.

And Allah knows best.