I like LRN the Lingo (.99), I think it does what it says in a straight forward and easy to use way.
What does the app do? It is a slang, text code, and emoticon dictionary of terms and keypad images in wide use by today's youth. The interface is well designed and allows you to search/translate if you have code in front of you like <:-P. which means party tonight, to which you may want to respond to that teen - since it's a Monday with; YBS - you'll be sorry. I had been searching for one of these apps so when the developer offered me a code, I had to give it a try.
I've been using this app for awhile now, giving my friends a shot at using it and pretty much everyone likes it. When you open the app you go directly to a menu and search screen which lets you look for text, lingo aka slang, and emoticons. The various emoticons are probably my favorite since there were a lot I didn't know and I find myself dropping them into Twitter or text messages. While you can certainly go on line and look this stuff up for free, for .99 and it's on your iPhone/iPod or iPad I think it's a reasonable price. On the down side, I did think that there were a lot of references to drugs, and firearms, possibly that's the youth culture today or maybe it was just how these particular codes, slang and emoticons were selected, I don't know, so be prepared. But isn't this good to know if you're an adult who's concerned what their kid has been texting all weekend?
I would certainly have reservations about letting a pre-teen use this app, though they may very well see or even use some of these terms, why introduce them before you have to. I think by the time a kids in Junior High and High School they've seen and heard all these things, though you - the parent, might not have.
What I'd like to see in a future edition is the ability to add new slang, codes and emoticons, and possibly update to some urban dictionary in the cloud so that the terms and translations stay fresh. Overall it's a nice little app, if you have teens or are a grandparent or maybe the Principle in a Junior High School, this is actually a useful app, CUL8R.