Is it legal to celebrate Mass in Latin?

Emphatically YES!

The Ordinary Form of Mass, the Novus ordo as promulgated in 1969 following the Second Vatican Council, may be said in Latin or in an approved translation. It is celebrated regularly in Latin, as well as in the vernacular, in St Peter’s, Rome, and in many cathedrals, abbeys and churches across the world. For a guide to such Masses in our own country please visit the Directory page on this website.

The official, definitive books of the Sacred Liturgy are always in Latin and all translations must conform strictly to the Latin texts. The Church has been adamant in requiring the use of Latin in the Sacred Liturgy to be preserved, particularly where people of different nations regularly come together, and that all Catholics should be familiar with the parts of the Mass that pertain to them. Please see the SUMMARY OF OFFICIAL DOCUMENTS ON LATIN on this website.

Use of the earlier, Extraordinary Form of Mass, sometimes known as ‘Tridentine’, is also permitted, using the Missal of Blessed Pope John XXIII (1962 edition), and may be said only in Latin, though in its most commonly used low form is often followed by prayers in the vernacular.”

Is the Tridentine Mass another name for the Latin Mass?
Why retain Latin in the liturgy of today?