The "Salah" prayer has to be done in Arabic, because the Quran (word of God) was revealed in Arabic!
Translations very per translator, and are in no way comparible to the true Quran, which is in Arabic!
Imagine if you translated Shakespear to an other language, it would lose much of it's essence, the same with the Quran (the perfect and divine book)!
So "Salah" prayer must be done in Arabic!
But other types of prayer, like "Supplication" this can be done in any language!
There is more than 1 way to pray in Islam!
Islam is a way of life, not just a religion!
And thus We have sent it down as a Qur'an in arabic, and have explained therein in detail the warnings, in order that they may fear Allah, or that it may cause them to have a lesson from it (or to have the honour for believing and acting on its teachings).
( سورة طه , Taha, Chapter #20, Verse #113)
RECITATION IN ARABIC IS NECESSARY FOR "SALATH"!