In our city a Christian sister converted to Islam. Now salat five times is Fard on her but she cannot read it in Arabic. Even if she try to Pray in Arabic she doesn't understand. Can she read salat in English. If she is allowed then why not I should pray in urdu although I am born Muslim but still I cannot focus on the meanings while reading it in Arabic Language. Please give solid reason as I already do not agree with preservation of Islam in Arabic as what is the use of preservation when you cannot benefit from it. We should not worry about hifazat of Quran as ALLAH has already taken the responsibility. I am interested in solid reasoning from Quran and Ḥadīth.
There are two parts to your question.
As far as the convert is concerned, she can begin with the rituals of the prayer which of course do not require any language. eg qiyam, ruku and sujud. At the same time she should start learning the essential utterances of the prayer which have to be said in Arabic. (all other utterances like for example dua before the fatiha recital and dua in the qa'da can be said in one's native language). The essential utterances which have to be said in Arabic, as pointed out by Javed Ahmad Ghamidi are:
The prayer shall begin by saying اللهُ أكْبَر (God is the greatest);
Then Sūrah Fātih*ah shall be recited during the qiyām, after which, according to one's convenience, a portion from the rest of the Qur'ān shall be recited;
While going into the rukū', اللهُ أكْبَرshall be pronounced;
While rising from the rukū', سَمِعَ اللهُ لِمَنْ حَمِدَهُ (God heard him who expressed his gratitude to Him) shall be uttered;
While going for the prostrations and rising from them, اللهُ أكْبَر shall be pronounced;
While rising from the qa'dah for the qiyām, اللهُ أكْبَر shall once again be pronounced;
At the end of the prayer, السَّلاُمُ عَلَيكُمْ وَ رَحْمَتُ اللهِ (peace and blessings of God be on you) shall be said.
Learning the above would not require much time.
The second part of the question relates to why Arabic is essential in the prayer.
The simple answer to this question is that the Almighty could have adopted two ways in this:
1. He could have left us free to read the prayer in our own language
2. He could have bound us to read the prayer in a particular language, for example Arabic.
He instead adopted a third way which was an amalgam of both -- this would in one way unite the ummah in one and in another way leave them independent. So God prescribed certain essential utterances in Arabic and some other ones which one can read in one's own native language.