Valloric thank you for this really detailed guide.
The reason I wanted to change fonts of my 505 was not that I dislike default fonts but I had a problem with three of Turkish characters (Şş İı Ğğ) I thought changing fonts would help me solve this problem.
My firmaware was 1.1.01.25200. So first I had to downgrade it to 1.1.00.18040. (Version.dat trick worked well). Then I followed your guide step by step and managed to change the fonts.
I used
Constantia for Swis721 BT,
Cambria for Dutch801 Rm BT and
Calibri for Courier10 BT.
It worked well or so I assumed at the beginning. Fonts of the menu and text were changed as I desired but still I did not get those Turkish characters shown up correctly and now I had this additional problem;some of my files (I was using Word Doc files and transferring them with eBook Library) caused reader to reboot.
Only after hours of playing with fonts and trying different combinations I realised that those Turkish characters I was in pursuit of were actually present inside the original fonts.
That's when I decided that my problem was not about fonts.
I flashed my reader back to original firmware 1.1.00.18040 (Since there is no official installer for 1.1.01.25200 I can not update to that, I guess. OR if anyone knows a way to get back to my original firmware (1.1.01.25200) that would be much appreciated.)
Then I found here this software everybody was taking about;Calibri. I used it to convert my files to LRF and Voila! Now I can see all the Turkish language specific characters as well without a problem and if I feel to read in different font I just embed them to LRF file. One last thing, I tried same LRF file with and without embedded font and to be honest I couldn't see any much increase in page turn time with embedded fonts. (Maybe very very slightly slower but really it is nothing to mention about)