Translation feature is currently available for 40 languages only and it will run on browsers installed on Apple iOS device, Android and Twitter's very own Tweetdeck client only.

It is very easy  to use the tool. Users can click on a tweet, click on a a tiny globe-like icon that later appears which will prompt the Bing translator to translate the user's chosen default language. The user will be able to see the original tweet on the top of the translated tweet. The translator can be turned off and on by signing into the Twitter account on a desktop computer or a laptop. Once the users check
the "Show tweet translations" option on the settings page, the feature will appear.
 
The globe-like icon at the side indicates that the tweet was originally published in a different language
and that the translation is available. And the Bing translator is far from being perfect, and the translations may have margin of error.