Cypher Language

The writers need a new language. But they don't want to actually invent a new language. So they make the "new" language a cipher of English -- usually, a substitution cipher -- with the same words, grammar and all. Typically, an entirely new 26-letter alphabet is invented, but occasionally "cryptogram"-style ciphers are used, as in Final Fantasy X and Order of the Stick.

Works from non-English-speaking countries may do the same with their own language or alphabet, but not always.

See also Wingdinglish. For when this happens to the language's grammar itself, see Re Lex.

Anime and Manga

 * Digital World writing in the first three seasons of Digimon is also a cypher of katakana. (The fourth season only uses three or four symbols.)
 * Haibane Renmei has an ancient alphabet which is basically written sign language.
 * The runes of Madoka Magica. Comes with three variants!
 * Dog Days has a cypher of katakana. That they use to spell English words.
 * Rave Master has the dead language Symphonian, which substitutes hiragana for characters made up of English letters. For example, the symbol for 'ka' becomes a sideways 'K' with an upside-down 'A' on top of it.

Comic Books

 * The Legion of Super Heroes uses a substitution-cipher font to represent the future language Interlac; both the comics and the cartoon series use this for in-jokes.
 * Superman's home planet Krypton's language has a substitution cipher.
 * Marvel's Doopspeak (the language spoken by the character Doop from X-Statix) was a substitution cipher using the font "Roswell Wreckage".
 * The Blue Beetle scarab's language was originally represented by a substitution cipher, but eventually transitioned over to English. In a clever move, during the transition, they used an alien-looking font in a style that resembled the substitution cipher, but whose characters could be made out as the Roman alphabet.
 * The "Symbion" alphabet in this Merchandise-Driven comic from The Eighties is not only a substitution cipher for the English alphabet, but based closely on, of all things, the cipher used by the Freemasons.
 * In X Men, one member of the Starjammers' thought are expressed in what looks like a cipher, but if viewed carefully, turns out to be very oddly-lettered English.
 * The Shadow Strikes issue 1 did this for what was supposed to be Russian.

Film

 * The Vogon written language in The Hitchhiker's Guide to the Galaxy is a stylised version of Pitman 2000 shorthand
 * The Gelfling language in The Dark Crystal. We only hear a few lines, but it's pretty obvious.

Literature

 * Piers Anthony sometimes does this for the language barrier between Xanthians and Mundanes outside Xanth.
 * The Artemis Fowl series has lines of Gnommish and Centaurian running along the bottom of each page (ommited in some U.S. editions.) Rather than being graphemes of a full-on Con Lang they constitute a Cypher Language offereing secret messages to those who decode them.
 * Though this is only applicable for the codes along the bottom of the pages- in-universe, Colfer instead makes them completely seperate languages.
 * Aurabesh (sometimes Aurebesh) in Star Wars. It has a few new characters for common two-letter combinations like "th", but whether they get used varies.
 * Dinotopia's footprint alphabet, supposedly invented by small three-toed dinosaurs running on wet sand.
 * Even JRR Tolkien was not above this. The writing on the map in The Hobbit is plain English, written with Old Norse runes as a simple substitution cipher. If you already knew the runes (this Swedish troper learnt them in fourth-grade history class) it wasn't that much of a cipher. To be fair, he was supposed to have been translating the Red Book in the first place to get the Hobbit. At least, he was by the time he finished Lord of the Rings.
 * This is blatantly stated in the LotR title page. The Cirth at the top reads "The Lord of the Rings, translated from the red book" while the Tengwar at the bottom continues, "of Westmarch by John Ronald Reuel Tolkien. Herein is set forth the history of the War of the Ring and the return of the King as seen by the Hobbits."
 * Most of the people who use tengwar in Real Life are using it in this context, rather than using it to write actual Elvish languages, though the better ones at least make a set of phonetic rules to write English in rather than substituting English spelling.
 * Converting the Hebrew characters of "golem language" statements in Making Money reveals that it's in English, although spelled phonetically in part.
 * There was a mystery novel that did this in what was supposed to be Coptic. (I forget the name or the author, but the protagonist is a female lawyer in 1880s San Francisco.)

Live Action TV

 * The Hebrew alphabet is used for this purpose in the Aussie version of 'The Amazing Race'.
 * The creators of Stargate made a cypher to function as the Ancient language during production of Stargate Atlantis. It even fed back into the main series, though obviously episodes from before the premiere of Atlantis don't use the actual cypher, but are just "made up as we go" blocky-looking symbols. Stargate Universe uses the cypher, too, drawing most attention to the numbers of the countdown clock. Enterprising viewers have created a font called "Anquietus" and some fans are fluent in written Ancient (which isn't as hard as it sounds; it could easily be learned in a day and mastered in a week).
 * In Kamen Rider Kuuga, the untranslated language the villainous Grongi speak is a simple substitution cipher of Japanese.
 * They also added a sentence structure switch that only existed part of the time.

Tabletop Games

 * When Games Workshop released Tau, they used such an alphabet for the Tau's language.
 * Used for elvish and dwarven scripts in some Forgotten Realms products.

Toys

 * Bionicle is a borderline case. It claims that the characters are speaking a different language, but it also provides a 26-letter alphabet with stylized, circular letters, and most of the written text in the canon consists of English words written in the Matoran glyphs. Then again, this may still be the Translation Convention at work.

Video Games

 * Al Bhed from Final Fantasy X. Happily, the cypher is designed so that the replaced letters can (usually) be pronounced phonetically and still sound like a real language, both in English and in Japanese. It had to be, since there are some voice-acted parts in Al Bhed.
 * Final Fantasy X also features three written scripts, dubbed Spiran, Yevon, and Al Bhed by fans. They're all English alphabet ciphers.
 * Hylian is like this in Zelda. More specifically, it's a code for Japanese kana in The Legend of Zelda Ocarina of Time and The Legend of Zelda the Wind Waker, and a code for English in The Legend of Zelda Twilight Princess (though flipped right-to-left in the Wii version).
 * In The Elder Scrolls series of PC games, Daedric is a substitution cypher of the alphabet, with symbols replacing letters. However, Daedric runes are not arranged like Latin letters - it's quite common to see writing in Daedric written vertically or with runes superimposed over others. In a similar vein, there's the Dwemer language seen in a few books (though it's completely meaningless, in that case), but becomes similar to Daedric cipher in Oblivion.
 * The dinosaur language "Saurian" in Star Fox Adventures -- in fact, the key to decode it is even given in the game's manual.
 * Melnics in Tales of Eternia looks graphically like angular, runic Sanskrit, but it's a (good) English cipher.
 * Many Tales games have text which are cyphers, or in the extreme cyphers where the new letters actually look similar to they're English counterparts, making it actually fairly legible if you look hard enough.
 * The "Galactic Alphabet" in the Commander Keen series simply substitutes symbols for English letters. Episodes 3 and 6 contain translations of the entire alphabet hidden in secret levels (a secret island in episode 3, and a space station in episode 6). The alphabet appears to have been designed to be written with a calligraphy pen, but with slight modifications to a few letters it can be written with a normal pen.
 * A Metroid Prime 2 design sheet (viewable in one of the game's bonus galleries) gives a complete set of 26 three-dimensional Luminoth characters and their English alphabet equivalents. They actually work in-game; the Luminoth Lore images are 3-letters that have some relevance to the lore in question. Indeed, the last image in the game's bonus galleries is a very long message in Luminoth script. One that has sadly been untranslated, because translating 3D text on a 2D image is really hard.
 * The Elites' language in the original Halo is English played backwards and distorted. In addition, backwards messages from the Gravemind are hidden in "Mausoleum Suite" from Halo 2, and "Black Tower" and "Gravemind" from Halo 3.
 * The Strogg "Language" in Quake IV
 * In Quake II, it was just English in a Foreign Looking Font.
 * In Space Quest 3, Roger can view a secret message for getting a high score on Astro-Chicken. If he uses his Secret Decoder Ring on it, he discovers it's an English cipher.
 * In Final Fantasy Unlimited, the native language of Wonderland is a cipher of English. If you want the key, though, you'll have to track down the (out-of-print) artbook.
 * Precursor/Old Precursor, a substitution cypher from the Jak and Daxter series.
 * Similiarly, the Ultima series employed a number of these (such as Britanic runes, Gargish, and Ophidian), which were mostly substitution cyphers given in the manuals. It used to be that being able to read Britanic runes marked you as a dedicated (retro)gamer, while knowing D'ni marked you as insane. That was years ago, so both are now likely to signify the latter.
 * Fire Emblem: Path Of Radiance and Fire Emblem: Radiant Dawn use a strange curvy alphabet for the "old tongue", which is used primarily by heron and wolf laguz. It's a cypher, but the game never provides the key. Translating it can produce a form of Bilingual Bonus; particularly Leanne's support dialogue, where most of what she says is actually her complaining about not being able to speak modern languages well (which actually doesn't make a lot of sense if you support her with someone who speaks to the old tongue.)
 * The Bilingual Bonus with Volug's support reveals he is actually one of the funniest characters in the game. For example, wondering aloud if everyone would be so shocked as to stop fighting if he eats an enemy.
 * The script in Aquaria, a substitution cipher.
 * Lazy players can replace the graphics file holding the glyphs for the Aquarian alphabet with one containing English letters, and have almost all of the text in the game translated, except for a few bits that are painted into the background scenery.
 * Breath of Fire: Dragon Quarter used a pseudo-Cyrillic alphabet for writing in the game. Not used in game mechanics, but the game creators ended up putting a lot of Easter Egg notes in the game itself as well as official artwork.
 * La-Mulana has what would otherwise be ordinary Arabic numerals rendered in cipher symbols.
 * Nelly Cootalot uses the Piraglyphics system, where an improvised pangram would be translated into an ordinary alphabet, thus scrambling the letters. To make his particular version work, Bloodbeard used the initials of his pseudonym and the traditional signing "X" (along with intentionally misspelling a vital phrase).
 * Pokémon Mystery Dungeon uses 'footprint ruins'. While there's no actual direct-to-English alphabet translation ever given, it is amusing in that they are the actual footprint images designed for assorted Pokémon.
 * In Resident Evil 1 (not the remake), the second laboratory password is "Mole" written in the Runic (pre-Latin Germanic) alphabet.
 * Twisted Metal: Black uses a simple numeric substitution cipher for Minion in his Story mode's loading screens.

Web Comics

 * Uryuomoco from El Goonish Shive is a cypher with way more complicated rules than most of these, ensuring that the result is "foreign-sounding" gibberish pronounceable by English speakers.
 * Played literally with Haley's "cryptogram-speak" gibberish from Order of the Stick, with a different translation key each strip.
 * Hannelore's Black Speech from this Questionable Content strip, which translates into
 * Homestuck uses a flipped version of the Daedric alphabet from The Elder Scrolls for its Alternian script.

Western Animation

 * The Legion of Super Heroes uses a substitution-cipher font to represent the future language Interlac; both the comics and the cartoon series use this for in-jokes.
 * An alien language invented for sight gags in Futurama used this, being a straight letter-replacement for English. It would frequently show up as graffiti or on signs that viewers could interpret to get an extra joke. A second alien language (AL2, to obsessed fans) was invented in the second season, using a much more complicated mathematical substitution, because the writing staff are a bunch of massive nerds.
 * The Canadian Series Dragon Booster has its dragon script. Again, it's a substitution-cipher font.
 * According to Word of God, the written language in Storm Hawks is this and can actually be deciphered if one looked hard enough.
 * Transformers: Beast Wars featured separate alphabets for the Maximals and Predacons, both of which were ciphers for English with rather elaborate systems for writing numbers. They were used to insert a few easter eggs into the series.

Real Life

 * The "Maraglyphics" that adorn the wait queue for the Disneyland attraction Indiana Jones Adventure are a simple substitution cipher. The park occasionally distributes cards bearing the translation.