Yes, Andrey is right. It is not yet possible to use the Aptana settings.
I use a manual trick, although this is not something technical. I do this on my Aptana Studio 3.5.0 installed on Linux Ubuntu 12.04. Not sure if this will fool another OS.
I just copy any UTF-8 Hindi test, just paste it at the top of my PHP file. This code is not technical, it is just for example. This has nothing to do with the coding or preferences of Aptana.
Example:
<?php // हिन्दी ?>
, , , .
