When Android 4.1 Jelly Bean was rolled out to the general market, it did introduce limited support for bidirectional text in TextView and EditText elements, which enabled apps to show off and edit text in both left-to-right (LTR) and right-to-left (RTL) scripts. Well, the introduction of Android 4.2 Jelly Bean did bring something new to the table (and not just one new thing, I might add), including full native support for RTL layouts, where among these will include layout mirroring, so that you are able to deliver the same great app experience across the board, regardless of whether the language of their choice relies on a script that reads right-to-left or one that reads left-to-right.
Should you remain indifferent and do nothing, your app will remain the same, and it will, of course, continue to look as it had always been. Google is strongly encouraging you to perform a few simple changes so that the app will be automatically mirrored the moment the user decides to switch the system language to a right-to-left script (here are a few examples, Arabic, Hebrew, or Persian).
The world is, after all, a global village, so it pays to be nice to your neighbors.