Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: Although Arabic is the language of the Qur’an, the final revelation to humanity, and, as such, every Muslim should consider learning it a priority, there is nothing in the sources to indicate that learning Arabic is a pre-requisite for being a Muslim; nor do we know of any recognized scholar of Islam who considers it a pre-requisite for being a Muslim.

The definition of a believer is one who believes in Allah and the angels, the Books, the Messengers, the Last Day, the fact that good and bad are decreed by Allah; as regards practices, a believer upholds the five fundamental pillars, namely, the five daily prayers, offering Zakah, fasting the month of Ramadan and performing Hajj—provided one can afford it.
there is no other stated requirement for being a Muslim; Allah says, (Whoever surrenders his purpose to Allah while doing good works, they will surely have their rewards with their Lord, and they will have no reason to fear or grieve.) (Al-Baqarah 2: 112)
In conclusion: It is absolutely wrong to insist on knowledge of Arabic as being an absolute requirement in Islam.

Shedding more light on this issue, we’d like to cite for you the following fatwa:

As for making Arabic compulsory for all Muslims, this is a rather complex question. It is Allah who has made us speak different languages. He says in the Qur’an that this is one of His signs which manifest the greatness of His creation. He puts it on the same level as other signs such as the creation of the heavens and the earth. He says: (And of His signs are the creation of the heavens and the earth and the diversity of your tongues and your complexions. In all that there are signs for those who are endowed with knowledge.) (Ar-Rum 30: 22)
What is required of every Muslim is to be able to read surat Al-Fatihah and some other passages of the Qur’an in Arabic to enable him/her to offer his/her prayers. However, it is to the advantage of every Muslim to understand Arabic, because that would enable him to have a better insight into his faith. There is no doubt that you will understand the Qur’an and the Sunnah better, if you know Arabic. This applies to any work which you may be able to read in its original language or in translation. No translation could give an exact meaning of the original text because of the different associations and connotations of the words used in each language.