After taking a look at that website, since these are complete firmwares, they can be pushed over ADB after putting the phone is bootloader/download/fastboot mode. Once done, you'd have to issue a set of commands to flash the firmware. Here's a nice tutorial [Tutorial] How to flash a new boot.img via Fastboot Although its for a different device, underlying ADB commands are still the same.
Having said that, here's a nice discussion thread. [Q] Enabling other languages? Post 3 would be of importance to you. Its for a different device but the steps listed are just the same for you.