If you are a new Muslim and you don’t speak Arabic you are not obligated to speak Arabic. However you are obligated to speak it while in prayer. You must recite salat (prayer) in the Arabic language. It is encouraged to learn the language, both to speak it and to read it since the Holy Qur’an is in the Arabic language.
The Arabic language is a complicated language and some of which can not be properly translated into English or other languages, thus it’s importance to learn it so that you could better understand the Qur’an and to achieve better concentration while in prayer.