i think yoshi-p knows how to listen, read and talk in english but prefers to use japanese when he makes his keynotes and interviews because it's his native language and it's a language he can better convey his thoughts and express himself more compared to using english (which may be his 2nd or even 3rd language). i think it's the same case for everyone, you'd prefer to be spoken to in your native language so you can better understand and express yourself
