A recent update the Google Translate
application for Android 2.3 or greater has added the ability to use offline language packages when a connection to the Internet is neither practical nor cost-effective. The offline packs are called "less comprehensive than their online equivalents" on a blog post announcing the new feature, and weigh in at about 125MB per package. Languages listed as now available are French, Spanish, Chinese, and Arabic.
tried the Spanish and French offline package on a Galaxy S III and found it suitable for navigation, finding basic services, and most general uses for a traveller. Very specific terms or scientific terminology were missed, but translated properly with the online version of the translation library.
Also added to the app with this revision is vertical text translation of Chinese, Japanese, or Korean when used in conjunction with a device camera. An iOS version supporting the offline packages is not yet available.