Speaking as someone who goes to the Latin Mass almost exclusively, I'd answer (perhaps surprisingly) that actually the Mass *doesn't* have to be in Latin. The issue is much deeper than that.
When they switched the Mass from Latin to English they also completely revised the liturgical books. The Mass changed so much between 1962 and 1970 that they essentially created a completely new liturgy with new texts, new postures, new folksy music instead of chant, etc....quite aside from the translation.
Many of us that have come to be dissatisfied with the 1970 liturgy have asked for (and received) permission to go back to the 1962 books, which was still in Latin. We find it more reverent, more conducive to prayer, and generally more true to Catholic doctrine. And many of us love the Latin language too, no doubt about that. :)
That said, if an English version of the traditional liturgy were available, I would be quite happy. When they created the Anglican Ordinariates we actually got something like that. I do attend those Masses on occasion and find them vastly superior to the 1970 English Mass. Anglicans have been *much* better than we have about making English sound beautiful and reverent.
Also, since some of the greatest liturgical texts have been written in Latin and attracted the interests of great composers (Dies Irae, Mass settings, etc.) it seems really myopic to completely sever that connection. We have 1500 years of beautiful Latin music and compositions....why throw those out?
In the Latin mass, is the entire church service(the complete liturgy, the singing, the responsive reading and the homily) all in Latin or just the part of the service dealing with the Eucharist?
Thanks.