This actually gives a clue to a long-standing question: how much do the osa-yukkuris understand of what's being said by the regular Touhouites?
In this case, them understanding Iku's joke about finding her a husband (even if they don't realize it is a joke) says the level is pretty high.
Santaaaaa!Shake Tremble#1183 Iku-san's WishHuh? What is it?You guys are going to give me a wonderful guy that I can spend the Christmas with?Shake TrembleI can't believe it!Shan Shan ShanShake TrembleWait a sec! I was merely joking! Why are you guys running away?!!