Hi,
I have some problems with spécials caracters on my OSMC like the artist “Aṣa” who are display like “A▯a”
How resolved this issue ? Don’t said me to rename “Aṣa” with “Asa” 
I want see “Aṣa” 
If you mean the problem is with how Kodi displays them, first make sure that you have the language set correctly.
Settings - Interface - Regional - Language
Also, not all fonts support all characters, so change to the Arial font:
Settings - Interface - Skin - Fonts