I've looked at some translation apps before, and it seems each time I review a new one I see increased capabilities and better performance. iTranslate Voice has available on the iPhone for awhile, and now it has come to the iPad in an HD edition.
Like its smaller sibling, iTranslate Voice HD can translate 31 languages both directions. Some of the 31 are variations or dialects of one language, like Spanish, that appears in Mexican, Spanish and US versions.
Operation is simple. Speak into the iPad microphone in your language, and out comes the selected language in your choice of a male or female voice. Another nicety is that you can control the speed of the translation, which is really quite helpful when you are learning a language. You can also use the app like a dictionary, and look up words for definition. Translations can also be copied to the clipboard and mailed. For all its features, you need an internet connection because the heavy lifting of recognition and translation are done on remote servers.
If you don't want to speak, you can type your words in, or correct any recognition errors. The app is powered by Nuance speech recognition, which is also providing the same service for Apple's Siri. The translations themselves are done by Microsoft.
In my testing, things went pretty well. My high school German came back as reasonable English, and my tests with English to Spanish looked solid. Speed is very good, so if you are in a foreign country or speaking with a non-English person, you can move along with a conversation reasonably fast.
iTranslate Voice HD is on sale for a short introductory price of US$0.99. Of course Google Translate is free and supports 64 languages, but I've had some network issues with it and it doesn't seem as smooth and feature rich as iTranslate Voice HD.
The iPhone version of this app is separate, so you have to buy again for the iPhone. If I was traveling, the iPhone version would make more sense, with only the larger and louder speaker on the iPad making sense of the idea of carrying an iPad around. Either version of the app works well, as long as they cover the languages you need.