until you get a better reply, did you see this message in your terminal?
The extension is at /mnt/sdb1/tce/optional/mylocale.tcz and in onboot.lst
Reboot with lang=xyz (for example lang=sd_IN@devanagari) to start using this
--change /mnt/sdb1 to where ever you have TCE mounted
2) so you have rebooted after verifying your onboot.lst has that TCZ loading?
and you have editted your bootloader .....pretending you use grub you append to your kernel line
"lang=sd_IN@devanagari" without the quotes
3) now on reboot...open terminal as a local user and try this command and report what you see pls
locale
If you don't see then its likely terminal lang won't change.
4) Firefox is US lang what you need if you can afford the download is to download a specific version tarball
--unpack it in your home folder
click on run wbar icon and try /home/yourname/firefox/firefox
there are a few Indian types here
http://www.mozilla.org/en-US/firefox/all/good luck