You'll often find the Liturgy chanted with a mix of Coptic, Arabic, and the language of the place (e.g. French when in France, English when in the U.S. etc.). Some priests even switch between languages within the same paragraph. In some parishes you'll find that they dedicate entire Liturgies, on a regular basis, to being chanted in the language of the place so as to permit the younger generation to follow easier, but even then you're bound to hear some hymns chanted in Coptic.