One of the most popular languages used to make something seem ominous, mystical or scientific is Latin. As the language used by Catholicism, it can carry heavy religious tones depending on context, which is often associated with magic. It's also a common language used for scientific nomenclature, such as species taxonomy ie. homo sapiens and felis domesticus being humans and house cats respectively.
However, Latin is an old language and one that is no longer spoken as anyone's native language. People will still teach it, the Catholic church uses it and it's the root of numerous living languages today, but Latin itself is pretty dead. Despite this, it carries an edge of importance, classiness and an association with religion and magic. As such, many writers are fond of inserting Latin into their stories for any number of reasons. The fact that it may not really fit in or seem out of place isn't really relevant: Frankly, it just sounds cool.
Of course, for every writer who succeeds in spicing up their story with a little Latin, there are probably three that simply make the reader cringe or at best roll their eyes: The use of Latin has also come to seem pretentious and no one wants to seem pretentious. And sometimes And sometimes writers are satisfied with just sounding vaguely similar.
Crazy Samaritan's suggested edits:
Latin carries an implication of importance, classiness and mysticism. Despite being a dead language,note it retains an association with magic, religion, and science. It is the language of those who know secrets and have uncovered ancient mysteries, and creators use it (or something that sounds like it) for those associations.
The Latin Language is still taught and utilized for many people and it's the root of numerous living languages today, making it both accessible for creators/audiences and maintaining the connotations with magic (Stage Magicians using pseudo-Latin incantations like "hocus pocus"), religion (Latin is the official language of the Catholic Church), schools and school-based organizations choosing a Pretentious Latin Motto, and science (The tradition of Greco-Romanism is most exemplified in the field of taxonomy). As such, many writers are fond of inserting Latin into their stories for any number of reasons. The fact that it may not really fit in or seem out of place isn't really relevant: Frankly, it just sounds cool.
This is a Sub-Trope to Gratuitous Foreign Language, where creators include foreign words (and close-enough foreign words) for a variety of reasonsnote . For help in parsing some of the Latin present in examples, please read the Latin Pronunciation Guide.