"Gloria in excelsis Deo et in terra pax hominibus bonae voluntatis." So goes the ancient translation into Latin of Luke 2,14 used in the hymnus angelicus at the Christmas liturgy of the 4th century. For centuries now it has been sung in churches almost every Sunday, but it still belongs especially to Christmas.
The classic translation of this verse into English is "Glory to God in the highest, and peace on earth to men of goodwill." While this translation is not inaccurate, it is in my opinion misleading. You see, before I knew any Latin, I had thought that the adjective "highest" modified an implied noun like "degree", so that the first clause meant something like, "Let glory of the highest degree be given to God". Now I see that the adjective "excelsis" modifies a plural noun, and that it refers either to high people or high places, so "in excelsis" either means "among the high [heavenly hosts]" or "in the high [heavens]." Since there is an implied parallelism with "in terra", the phrase seems to refer to high places rather than people, so a less misleading, though less literal, translation might be, "Let glory belong to God in the high heavens, and let peace belong to men of goodwill on earth."
Note that I supplied a verb phrase "Let ... belong" which is not explicit in the Latin. This is because in Latin the verb "esse" is commonly left out of sentences and clauses where it is clearly implied. While "esse" is usually translated into English as "to be", when its predicate is in the dative, as it is with "Deo" and "hominibus", it means "to belong to". So the Latin has "est" or "sit" invisibly inserted into the two clauses, and these should be translated as "belongs to" or "let ... belong to".
In English, when you leave a verb out of a sentence like this, that verb is strongly implied to be in the subjunctive mood. In Latin, it can also be in the subjunctive mood, but it is more likely to be in the indicative. In other words, the Latin could just as easily mean, "Glory belongs to God in the high heavens, and peace belongs to men of goodwill on earth."
So which translation is the right one? Since it could be either subjunctive or indicative, and since the author did not bother to explicitly state the verb, we can assume that he did not consider the distinction to be significant. In other words, both are right. The angels are expressing a wish that has already been fulfilled or is being fulfilled or whose fulfillment is inevitable.
This deliberate vagueness was exploited even more effectively by Saint Jerome in the 5th century, when he revised the Latin translation of Luke in his Vulgate. He did not follow the old hymn, but wrote, "Gloria in altissimis Deo et in terra pax in hominibus bonae voluntatis." We have "hominibus" changed to "in hominibus"; our second dative has become an ablative. This is significant; it drops us down to one implied "esse" from two. Now both the glory and the peace belong to God. "To God belongs glory among the most high and, on earth, peace among men of goodwill."
I have translated the two phrases "in altissimis" and "in hominibus" as modifying "gloria" and "pax" respectively, but both phrases may just as well modify "Deo", as in the paraphrase, "Glory and peace belong to God [who dwells] among the most high and [now] on earth among men of goodwill."
Emmanuel. God is with us. Merry Christmas.
Gloria in excelsis Deo et in terra pax hominibus bonae voluntatis. Laudamus te, benedicimus te, adoramus te, glorificamus te, gratias agimus tibi propter magnam gloriam tuam, Domine Deus, Rex caelestis, Deus Pater omnipotens.
Domine Fili Unigenite, Jesu Christe, Domine Deus, Agnus Dei, Filius Patris, qui tollis peccata mundi, miserere nobis. Quoniam tu solus Sanctus, tu solus Dominus, tu solus Altissimus, Jesu Christe, cum Sancto Spiritu: in gloria Dei Patris. Amen.