All the text that appears in the widgets of your Viral Loops campaign (eg. in the popup or the Sharing Widget) as well as the content of the emails sent from your campaign can be edited. That way, you can change that text to any language you wish.
Here's a preview of the Viral Loops popup in vietnamese:
(pardon the translation from Google Translate)
However, the widgets are not yet multilingual, ie. it is only possible to display them in one language at a time.