Twitter Officially confirms Bing Translation for your Tweets
Twitter has partnered with Bing to translate tweets. Now users will be able to see tweets in multiple languages by using Bing translator.
— Twitter (@twitter) January 22, 2015
If you see a tweet in some foreign language, tap on the global icon located in the tweet. A translation of the tweet will appear below the original tweet.
Twitter also wards that the translation engine relies on advanced translation software, results still vary and there may be errors. This is why original tweet will always be there.
Tweet translation feature is available on Twitter.com, Twitter for Android, Twitter for iOS and Tweetdeck.