Complex sentence: Latin liturgical rites used within that area of the Catholic Church where the Latin language once dominated (the Latin Church) were for many centuries no less numerous than the liturgical rites of the Eastern autonomous particular Churches.
Split into simpler sentences: Latin liturgical rites are the Catholic liturgical rites used within the Latin Church (that part of Roman Catholicism originating in the area where the Latin language once dominated). The Latin rites were for many centuries no less numerous than the liturgical rites of the Eastern autonomous particular Churches.