Feat tax for eastern weapon?

[TimD]

No, you could just use a rapier (which is a martial one-handed piercing weapon, not a light weapon) rather than a wakizashi (which is an exotic light piercing OR slashing weapon with the deadly special property) or play a class that gives you a wakizashi proficiency (samurai, ninja) or select a racial option that gives you a proficiency.

What you are asking about is called "re-skinning" and there are very few legal options to re-skin in PFS.