Assalam alaikom Brothers and sisters, thought this might help reverts with questions asked by themselves or family.
Why Is Salah (Prayer) in Arabic Only?
The simple answer is that the Qur'an was revealed in Arabic and not one verse (Ayah) has been changed since its revelation. The form of Salah is taken from the example of Prophet Muhammad, pbuh. One of the requirements for the Salah to be valid is that Surat-Al-Fatiha be recited in every Raka (prayer cycle). Surat-Al-Fatiha is the opening chapter of the Qur'an and is, of course, in Arabic. It is revealed within the Qur'an itself that it is an "Arabic Qur'an".
To recite it in any other language would be in direct violation of the requirement because whatever was "recited" would only be one particular person's opinion of how that passage should be translated. The danger could continue on so that someone could hear what was recited in English and decide to translate it into French, leaving more meaning to be lost. Then, possibly someone would hear the French and want to translate it to Russian, leaving the original meaning literally lost in the translation, as has occurred in the Bible. (Jesus, peace be upon him, did not speak the Queen's English - nor King James', to be exact).
What Is the Non-Arabic Speaking Muslim to Do?
The short and obvious answer would be - make an effort to learn Arabic. However, that is not something that can happen overnight for most people. There are numerous parts of the Salah during which one can make their own silent supplications in their native tongue, in the meantime. It may help to try to pray in congregation as much as possible in order to hear it being read by the Imam during the prayer (Salah).
The most important Surah (Chapter) to be tackled by the new Muslim is Al-Fatiha. This can be memorized along with the meaning. To start off with, it is acceptable to hold a paper with the transliteration (if needed) on it during Salah, until it is memorized. The next task is to memorize another small Surah, taking things one step at a time.
Salah Isn't Meant to be a Hardship
The companions of Prophet Muhammad, may Allah be pleased with them, had the habit of only studying 3 ayahs at a time - they would not move on to the next three until they totally understood the first. It is not a race and not intended as a difficulty. It is more important that one feel the "silla", (the connection), during Salah then be stressing over trying to memorize everything at once in perfect Arabic.
The importance of Salah is stressed over and over in the Qur'an and in many different contexts in order to underline its importance in our lives - spiritually, mentally and physically. True believers are associated with patience and Salah (especifically Salah, not du'a). Possibly a good solution would be to make Du'a about perfecting Salah.
Quran: English Translation and Commentary; Presidency of Islamic Researches, IFTA, Call and Guidance; King Fahd Holy Quran Printing Complex, 1411 AH