Today, Microsoft Bing team released their Translator app for Windows Phone 8 devices. Translator app for Windows Phone 7 devices got over million downloads and high ratings. Bing team has now optimized the app for Windows Phone 8 with support for Lens feature. It has features such as Augmented Reality Translation using your camera, speech & text translation, word-of-the-day live tiles and a travel optimized offline mode in the app, etc,.
You can download from the marketplace here.