HoangLee: why are you trying to copy the font file into the read-only filesystem when you've been told to copy it into /storage/.kodi/media/Fonts ?
Simply, there is not directory "Fonts" in /storage/.kodi/media/
I have to use find command line to search where is the font arial.ttf so I did that.
OK, fixed the missed characters in the default fonts by Window arial.ttf
Now, I am happy with libreelec -kodi . Thanks a lot.