I think it was Cardinal Josef Tomko, the representative of the Holy Father to the Congress, who observed in a homily that he preferred the word "universal" to that of "international" to describe the Eucharistic Congresses. The Quebec Congress had three official languages - French, English and Spanish - with translation into several other languages via FM radio and headphones (supplied as part of the Congress welcome pack) available at the main congress venue. Inevitably, the majority of the Congress participants came from Canada and the United States, with Latin America providing perhaps the next largest contingent (I saw groups from Mexico, Peru and Colombia). I rather take for granted the ability that I have to follow French as well as English, but for those with only one of the official Congress languages participation must not have always been that easy.
So, with the best will in the world, the Congress didn't quite manage to be fully international as far as languages and participating countries went.
However, there were a number of points in the Liturgy where Latin was used, not just once, but each day (except Wednesday, when Mass was celebrated according to the Byzantine Rite). At both morning prayer and Mass, the Our Father was sung in Latin. The opening greeting In nomine Patris and Pax vobis were sung in Latin, along with their responses. The dialogue Verbum Domini/Deo Gratias was sung in Latin after each of the Scripture readings, as were the Dominus vobiscum etc at the Gospel. The dialogue at the beginning of the Preface was also in Latin, as were the Sanctus (I think, for those who know about such things, it was Mass VIII - I liked it, anyway), the Mysterium Fidei and the Per ipsum. The Credo, too, was sung in Latin when it was used. The office hymn for morning prayer on the Monday of the Congress was the Veni Creator Spiritus.
The words and music for all of this were provided in the Liturgy booklet, which was important for those less familiar with the Latin. Other parts of each celebration mixed use of the three official Congress languages, with additional languages being used for the prayers of the faithful.
The singing of the Pater Noster in particular seemed to go very easily and readily. For me, it seemed to represent a moment at which the universality of the Church could be experienced, with most people seeming able to join in quite easily. I think Cardinal Tomko has a point about the word "universal" to describe these Congresses ...