AF2+2 text states Black Magic, so at the very least I'd assume it works for dark magic and may work for elemental and black-aligned enfeebles as well (break, bind, gravity, sleep, etc). Depends on whether they actually meant all black magic or if it was a typo for dark magic. Hard to tell since it doesn't affect recast. Might be able to rig something up with waits to check though.
Doubt it applies to anything but dark.
JP:
暗黒魔法の詠唱時間短縮-8%
Google trans shows this as:
-8% casting time reduction of dark magic
French:
Temps de lancement des sorts de magie sombre-8%
Google translates to:
Launch time spells dark magic-8%
German:
Sprechzeit von Dunkelmagie-8%
Google translates to:
Talk time of dark magic-8%