If you're traveling to a location where you don't know the language. Google Translate will translate words and phrases in more than 60 languages. For most languages, it even has voice recognition--when you speak a phrase, Google Translate will read the translation back to you for correct pronunciation. For translating signs, try Google Goggles. That app uses image-recognition technology to conduct a search based on a camera snapshot, or to translate words from signs in English, French, Italian, German, Spanish, Portuguese, or Russian.
Google Translate is available on Android and iOS. Google Goggles is available as a native app on Android, and through the Google Search app on iOS.