Just wanted to post another success story (PRS-300) and a little more info for others looking into this.
I used the
Russification Sony Reader 300 (ver. boroda) and it was as simple as it says. Insert the folder into the root directory and let it do the work. It doesn't change your settings or language currently on the unit (it removes Dutch and changes that option to Russian). In the about tab you will now have 3 new options.
Pressing 0 allows you to change the clock options (don't choose the tick options, kills the batteries)
Pressing 1 allows you to turn the side button usage on/off
Pressing 2 allows you to change the enter button to either shutdown/screenshot
Very happy with the new options. It's nice to have the clock showing, and even better to be able to turn the page by pressing 8. I hold the 300 with my right hand and it was a little clumsy to keep reaching down to turn the page, especially when the pad of my thumb was resting on the 8 button anyway
The only thing I didn't do that I wish I did was to back up the original firmware before flashing. But all is working well, so not too worried.