pf2e.fyi
From Pathfinder Impossible Magic, which isn't enabled.

Diacritic Fluency

FEAT 6
CONCENTRATERUNESMITH
Activity free action
Prerequisites one or more Diacritic runes
Frequency once per 10 minutes

When you intensify your attention, you can modify a rune with great speed. The next time you Trace a Rune this turn, you can also Trace a diacritic Rune on that rune.

Pathfinder Impossible MagicORC