How to change /system/fonts directory permission to writable in switch off mode?
As it seems you can access your device via ADB, you should be able to remount /system read/write to repair that file, using

adb remount


After that, you can copy the intact DroidSans.ttf to /system/fonts, overwriting the 0-byte-file. Following a reboot, /system will be mounted read-only again, and everything should be working.



In case that adb remount should fail with a "permission denied", you might wish to read How to remount /system as read-write in Android, which explains the manual remount process step-by-step. That would basically be:


get a shell on the Android device using either adb shell or a terminal app
become root using su
find out how and where /system is mounted, using mount | grep system
mount /system read/write using the information obtained, e.g. mount -o rw,remount /dev/block/&lt;device&gt; /system (make sure to use the device obtained in the previous step instead of /dev/block/&lt;device&gt;)
verify whether your remount was successful, again using mount | grep system
now copy your DroidSans.ttf to /system/fonts
either reboot, or simply remount /system read-only using the parameters obtained in step 3, e.g. /dev/block/&lt;device&gt; /system ext4 rw,relatime,barrier=1,data=ordered 0 0


Always make sure to use the device and parameters obtained from step 3, or you might completely mess up.