Sonys original firmware doesn't offer an option to switch the language. You will have to install the original US-Firmware to get the english language on the device.
Basically it works this way (
Follow the instructions at your own risk! In the worst case you will brick the device.):
- Download the original US-Firmware from http://esupport.sony.com/US/perl/swu-list.pl?mdl=PRS505.
- Use your Zip-program (WinZip, WinRar, 7zip, whatever) to extract PRS-505 Updater 1.1.00.18040.exe into a directory called PRS-505 Updater 1.1.00.18040.
- Edit the file PRS-505 Updater 1.1.00.18040\eBookUpdater\assets\updaterAssets\PRS Version.dat and replace the contained number (110018040) to 140023261.
- Then connect your PRS-505 to your PC and start PRS-505 Updater 1.1.00.18040\PRS-505 Updater.exe to install the original US-firmware.
After installing the US-firmware you could use
PRSCustomizer to customize your PRS-505 if you want...