By His Grace and Mercy, Allah has made embracing Islam a cause to erase the sins that were committed before it. When a disbeliever becomes Muslim, Allah forgives all that he did when he was a non-Muslim, and he becomes cleansed of sin.

If a person does not know Arabic, this does not affect his Islam, and it does not deprive him of the honour of belonging to Islam. So hasten to enter Islam, for no one knows when death will come. If learning Arabic was really an obstacle, you would not find millions of Muslims who are not Arabs, who perform the acts of worship with ease.

1- It is not essential to take shahadah (say the testimony of faith) before witnesses. Islam is a matter that is between a person and his Lord. 2- No marriage contract is valid without a wali (guardian) for the wife, but no non-Muslim can act as a wali for a Muslim woman. For more, see the detailed answer.