From Android Guys:
Google today rolled out a new feature in the Google Translate application for Android devices. What’s new? Oh, nothing… except the fact that you can translate yourself into fifty languages.
You can select [Offline Languages] in the app menu to see all the offline language packages available for download. To enable offline translation between any two languages, you just need to select them in the offline languages menu. Once the packages are downloaded, you’re good to go.
Sure, it’s not as comprehensive as the stuff you get with an internet connection, but it helps in a pinch!