Complex sentence: His officers met each ship as it arrived at Whampoa Roads, the landing spot down-river from Canton, where each ship was required to engage a "Chinese linguist," that is, a representative of the Hoppo, as go-between and interpreter.
Split into simpler sentences: His officers met each ship as it arrived at Whampoa Roads, the landing spot down-river from Canton. Each ship was required to engage a "Chinese linguist," that is, a representative of the Hoppo, as go-between and interpreter.