Please tell me how to change display language


I launched my web page
Thank you.
Next I want to change its display language to Japanese
So I tried General->Language setting.
But its failed about 20 % everytime.

So I want to change page language by myself.
At first.I want to change top page.

So I watch Templates And->Templates Editor.
But I cannot find top page
I read header.html ,but I cannot find “Videos”,"Photos* “channels” “Collections” 's diplay string.
Please tell me how to do it