M Translations join the existing M Suggestions features that are already built into Messenger for things like quick replies, polls, and sharing your location. The translation feature, which should be available now for users in the US and Mexico, will recognize when a user gets a message in a language that isn’t set as their default. Then, Messenger’s M bot will pop up and offer to immediately translate it. The feature had previously been available for users in Marketplace transactions, but it’s rolling out now to all standard Messenger conversations, too.
For now, translations only supports Spanish / English, but Facebook is apparently already working on adding other languages.