User blog comment:B214/Question and Answers 4/@comment-24866657-20141019162746/@comment-16281343-20141020075832

Issei used Dress Break and Bilingual after Rias returned Issei's EP.

He can't use those two techniques if he isn't a Devil and he can't use it in the first place with just his measly demonic power. He needs to boost first or use Balance Breaker to increase his overall stats.