Extinct languages
The latin interface is monumental and it makes Google more trustworthy and knowledgeable.
Artificial languages
Google in Esperanto is very laconic and it even offers the option to restrict your search to web pages written in Esperanto.
The Interlingua interface uses an auxiliary languages that was created as a common denominator for Romanic languages. "With Interlingua an objective procedure is used to extract and standardize the most widespread word or words for a concept found in a set of control languages: English, French, Italian, Spanish and Portuguese, with German and Russian as secondary references," explains Wikipedia.
Fictional languages
For Star Trek's fans, there's a Klingon Google. Klingon is an artificial language that has its own sounds, rules and words. "A small number of people, mostly dedicated Star Trek fans or language aficionados, can converse in Klingon. Its vocabulary, heavily centered on Star Trek or 'Klingon' concepts such as spacecraft or warfare, can sometimes make it cumbersome for everyday use — for instance, while there are words for transporter ionizer unit (jolvoy') or bridge (of a ship) (meH), there is currently no word for bridge (that you drive over). Nonetheless, mundane conversations are common among skilled speakers." Marc Okrand, who invented the language, explains more about its meaning in an interesting video.
Bork, Bork, Bork! is the language of Swedish Chef, a character from the Muppet Show. "Nearly all Swedish Chef sketches begin with him in a kitchen, waving some utensils while singing his signature song in a trademark mock Swedish — a semi-comprehensible gibberish which parodies the characteristic vowel sounds of Swedish. The song's lyrics vary slightly from one episode to the next, but always end with börk! börk! börk! as the Chef throws the utensils aside." You can find Swedish Chef sketches at YouTube and install a cool Firefox extension that translates the content of web pages to Bork.
Elmer Fudd is a cartoon character. "He has one of the more convoluted and disputed origins in the Warner Brothers cartoon pantheon (second only to Bugs Bunny himself). His aim is to shoot Bugs, but he usually ends up seriously injuring himself. His stock line is: Shhhhhhhh, be vewwwy, vewwwy quiet; I'm hunting wabbits, heheheheheheh, although it varies in certain cartoons." This Bugs Bunny episode shows Elmer Fudd trying to capture the "scwewy wabbit".
Language games
The Pig Latin language has its roots in Britain and was initially used by criminals as a simple way to encrypt their messages. The rules are simple: if the word starts with a consonant, it's placed at the end and is followed by ay; if the word starts with a vowel, way is appended to the word. For example, Web becomes Ebway.
Internet languages
Google's hacker interface was an obvious choice for a company with a culture that encourages hacking. According to Wikipedia, leet "is a written argot used primarily on the Internet, which uses various combinations of ASCII characters to replace Latinate letters. The term is derived from the word elite, and the usage it describes is a specialized form of symbolic writing." There's no unique way to translate words into leet, but some of the most popular rules are to replace letters with digits or other symbols that look similar (for example, g -> 6, o -> 0, l -> 7, e -> 3). A simple way to access Google's leet interface is to go to 600673.com.
Unfortunately, most of Google's recent services aren't available in any of these languages, so you'll only be able to see Google Search, Image Search and Google Directory. The Google in your language program, which allows anyone to translate the messages from Google's services, includes these languages, but the translations aren't live for Gmail, Google Video etc.