How can one help an atheist interested in Islam who speaks English, given the inability to explain much to him due to language barriers and insufficient knowledge of the topics, and what are the appropriate Islamic books in English to guide him?

A woman's invitation to a man should be disciplined by the legitimate Islamic controls. It is better for men to invite men, and women to invite women, due to the risk of fitna. A man can be guided to specialized organizations in inviting non-Muslims, or to da'wah websites, such as this website which contains an English section with fatwas introducing Islam, dialogues with atheists, and e-books where he might find what he is seeking.