Progress can and may have blinded you.

[Facultas Tempestas]

Well, yes, but no. Sort of. Most English words are at least vaguely derived from Latin, but English itself is in fact a Germanic language.

Anglo-Saxon is Germanic. Anglo-Saxon evolved into Old English. When the Normans invaded England they formed Anglo-Norman, which evolved into Middle English. Latin was added to it, and Modern English was the eventual outcome.

I also found this on Wikipedia:

"One of the consequences of the French influence is that the vocabulary of English is, to a certain extent, divided between those words which are Germanic (mostly Old English) and those which are "Latinate" (Latin-derived, either directly from Norman French or other Romance languages).
Numerous sets of statistics have been proposed to demonstrate the various origins of English vocabulary. None, as yet, are considered definitive by a majority of linguists.
A computerised survey of about 80,000 words in the old Shorter Oxford Dictionary (3rd ed.) was published in Ordered Profusion by Thomas Finkenstaedt and Dieter Wolff (1973)[35] that estimated the origin of English words as follows:

Langue d'oïl, including French and Old Norman: 28.3%
Latin, including modern scientific and technical Latin: 28.24%
Other Germanic languages (including words directly inherited from Old English): 25%
Greek: 5.32%
No etymology given: 4.03%
Derived from proper names: 3.28%
All other languages contributed less than 1% (e.g. Arabic-English loanwords)

A survey by Joseph M. Williams in Origins of the English Language of 10,000 words taken from several thousand business letters[36] gave this set of statistics:

French (langue d'oïl), 41%
"Native" English, 33%
Latin, 15%
Danish, 2%
Dutch, 1%
Other, 10%

However, 83% of the 1,000 most-common English words are Anglo-Saxon in origin. "


So, while English isn't a Latin language (Italian, French, Portuguese, Romanian, Spanish), it isn't exactly Germanic either. As to why the Sentinal is speaking Latin, even though there is a story-specific answer, we probably could just chalk it up to Bungie's love of using Latin in their games (Marathon Trilogy, Myth trilogy).