Skill regained: Language: Latin
Date: Day 82
Game won: Bone Witch's Game

Skill:

This skill gives Io back her knowledge of Latin - a general ability not just to translate common Latin phrases (a la her motto), but also enough functional knowledge to read pretty extensive paragraphs written in it.

Skill regained: Extensive science knowledge
Date: Day 52
Game won: Delriza's Game

Skill:

This skill basically turns Phi into a walking science encyclopedia, since every Zero Escape game needs at least one of those. Her knowledge will range from being able to explain quantum mechanics to antimatter reactions to dihydrogen monoxide jokes to the color spectrum to delivering a sad explanation of Archimedes' principle -- oh no wait, wrong Uchikoshi game.

tl;dr SCIENCE