Magical Foreign Words

When a language other than the character's main one is used to invoke magic or other Applied Phlebotinum. Can be a case of Gratuitous Foreign Language, or may just be a case of a second or archaic language being appropriated for the task.

Note also that fluency is not required—in fact, language used this way often seems to have had a few go rounds in the Babel Fish. The key here is that the language itself is not a constructed language; it's a case of simply using the "otherness" of a foreign tongue for the target audience to invoke an air of mystery or cool.

When Language of Magic and As Long as It Sounds Foreign meet, you get this.

Anime and Manga
A standard trope in many Anime and Toku productions.
 * In Cardcaptor Sakura. All the card names are in English, and the final word of the incantation to turn the key into the wand is "Release!". Not carried over into the English dub for obvious reasons.
 * Most of the characters in Kamichama Karin use Latin for their attacks and suchwhat.... except for Karin, who instead springs for Gratuitous English.
 * Magical Girl Lyrical Nanoha: Is a spell of Mid-Childa origins? Chances are good that it will be in English. Is a spell of Ancient Belka origins? Chances are good that it will be in German.
 * All magical spells in Mahou Sensei Negima are done in Latin or Ancient Greek, with a few done in Sanskrit, all of which are surprisingly well done. The rule of thumb is that the older the language is, the more powerful it is.
 * One Piece frequently uses foreign languages when characters are calling their attacks—including those involving Devil Fruit powers and normal acts. Just among the main characters we see attack names in English, French, Spanish, and Italian.
 * The incantations in Sailor Moon are usually Gratuitous English but come from everything from Chinese to Portugeuse as well - you'd think it would have been from the lost language of the Moon Kingdom, but the foreign babbling just sounds more stylish.
 * A lot of the spells/magic attacks in Sugar Sugar Rune are in French.

Comic Books

 * During the first volume of the ongoing Gravel, Bill is talking to a magician named Sykes who notes that many of his peers considered him quaint for treating the archaic terms he uses to count sheep as magical. Given at the time they're talking, Sykes is the most senior member of one of Brittain's foremost occult orders...

Literature

 * "Wizard talk" in Discworld is Canis Latinicus. The Animated Adaptation of Soul Music comes up with a suitable Canis Latinicus invocation for the Rite of Ashk-Ente, which was never actually described in detail in the books.
 * In The Dresden Files, it serves as a buffer, protecting the mind of the caster from the direct connection that using your own language would be. It doesn't have to be actual Latin or whatever - most of Harry's spells are in pseudo-Latin but his actual Latin is terrible.
 * The language used is pure preference, with other characters shown using pseudo-Egyptian, pseudo-Aztec, and pseudo-Japanese.
 * It's the pseudo-ness that's important: the more you know of the language, the less protection it gives you. People are known to make up their own completely nonsensical languages for that express purpose.
 * Harry Potter also uses Canis Latinicus for magic words.
 * This trope is justified in Patricia C. Wrede's Mairelon the Magician and sequels. It doesn't matter what language incantations are in, as long as it's not the native language of the spellcaster; if you try to cast a spell using your own native language, it becomes uncontrollable.
 * Poul Anderson's Operation Chaos states that "exotic tongues are necessary for the more powerful spells--which is why so many African and Asian students come here to learn American slang...."
 * In the first section of the book, the protagonist cobbles together an emergency spell using Pig Latin.

Live-Action TV

 * Buffy the Vampire Slayer had spells in English sometimes, but often used this trope as well. What language they used could vary---often the demon's back story would tie it to some particular culture, and the spell would be in that language. Latin was also common for generic magic.
 * Kamen Rider and Super Sentai often see use of Gratuitous English; such that when Samurai Sentai Shinkenger chose to go with mainly Japanese for its attack names, it stood out. Kamen Rider usually has the devices do this, though Kamen Rider Double is notable for the Fusion Dance duo that make the headlining rider using Gratuitous English and German to "sync" themselves for the Maximum Drives.
 * Shinkenger's aversion became a straight example when it was adapted into English as Power Rangers Samurai, as the magic system is still based in Japanese kanji.
 * Merlin uses Old English.

Video Games

 * In Fate/stay night, all of Rin's incantations are in German—though not necessarily good German.

Real Life

 * Real Life quasi-example: The incantation "hocus-pocus" is thought to be derived from the Latin "Hoc est corpus meum (This is my body)," from the Roman Catholic Mass. It is thought that, at the moment the officiating priest utters the phrase, the bread and wine are supernaturally transmogrified into the actual body and blood of Jesus Christ. Latin was / is, of course, a language that very few people outside of a few specialized professions know.
 * "Abra cadabra" is derived from the Hebrew "Avra v'davra," which translates to "I make and I do." (Yeah, kinda loses some of the mystery in translation.)