Swipe your finger along the left edge of the screen. This will increase brightness if you swipe up and decrease if you swipe down.

On some (old) phones you have to switch off “automatic brightness” in device settings to enable this feature.

Put your own background in png or jpg format into Wallpapers directory on the memory card of your device. Then it will be visible in “Colors & wallpapers->Background” section in FBReader settings.

By default FBReader uses system language for UI. Since version 1.7.7 there is an option “Inteface language” in “Appearance” section of the settings dialog.