If you want the testing fonts, you add:
/etc/apt/sources.d/fonts.list:
deb http://http.debian.net/debian sid main contrib non-free
and
/etc/apt/preferences.d/pinning:
Package: fonts-* Pin: release a=testing Pin-Priority: 600
(priority between 500 and 989 means "causes a version to be installed unless there is a version available belonging to the target release or the installed version is more recent")
and after you apt update, you have access to sid.