Salat has specific method and that is to be done in Arabic. Salat would be invalid in any other language. However dua can be done in any language. No matter where we are from we all learn at least the basics of salat in Arabic and this enables us to all pray together in unity despite a variety of people coming together who do not speak the same language. The convert must learn these basics of salat in Arabic and can write them down and use their notes in salat until they memorize them. They should also learn the meanings of what they say as well in order to get that connection through their salat.