android:layout_gravity
defines position of the view with respect to it's parent.
android:gravity
defines position of the child views of the current view.
So setting android:gravity will work for you
Also refer to following post to handle screens for multiple languages
How to get text direction in Android and change layout dynamically according to the direction?
Also try setting android:textDirection
for RTL.
For more info you can go through following link:
http://android-developers.blogspot.in/2013/03/native-rtl-support-in-android-42.html