In what language should I speak to my child, and how can I develop his Arabic language, taking into consideration that I live in a Western country and my husband and his family do not speak Arabic?

Accustoming children to the Arabic language from a young age is a good and beneficial matter for their religion and character, for language influences the mind, religion, and character. It also increases resemblance to the Companions and the Tabi'un, and it is a part of religion, and knowing it is an obligation for understanding the Book and the Sunnah (definition).