The Pocket Monsters anime originally used Japanese writing for on-screen text and signs. A pain in the ass if you need to localize the cartoon into other languages. So the Pokémon folks came up with a solution: a made-up language. A Pokélingo, if you will.
Starting with anime series Pocket Monster Best Wishes!, the anime series began using a made up language that actually means something. So this sign from Best Wishes! episode #49:
Actually isn't just gibberish! It reads "Pokémon". Can't you see it? This is the language used in the Pokémon region of Unova, making it Unovan. Website PocketMonsters.net has an extremely helpful dictionary for deciphering the symbols, which directly correlate to English letters:
This is the main language used in the Pokémon anime; however, there's also a second and a third language. You can see their deciphered symbols on PocketMonsters.net.
PocketMonsters.net updated its dictionary early last January. Deciphering work began in 2011, with those involved on the project posting on the Serebii forums.
This week, another group—students from University of Kyoto's "Pokémon Club"—are saying how they've independently cracked the anime lingo, posting examples of how they've translated the Pokéspeak.
While this notebook is written in Unovan, the sentences are in English. The University of Kyoto students note that there are some mistakes. In one instance, "you" is written as "u", and "wha" is written instead of "what".
What's interesting about the deciphering done by the University of Kyoto students is how sometimes Unovan can be deciphered to reveal not just English words. For example, in this image, each Pocket Monster has its original Japanese name listed, with short descriptions in rough Latin script, like what's used to write Japanese (romaji).
So next to Deino (née Monozu in Japanese), it reads, "Mitame ha tyotto kimoi ne", which would be 見た目はちょっとキモいね in Japanese and means "Its appearance is somewhat creepy".
Pokémon people have created a language that people can decipher and read. Since the anime is then dubbed for different regions, that would mean Unovan isn't necessarily English, and it's not necessarily Japanese—which is proved by the written language having both in it. This means that spoken Unovan could then have its own pronunciation. So somebody create a pronunciation guide so people can congregate in public and speak Pokélingo. Cuter than speaking Klingon!