He's too afraid to try.. you know, sometimes when we're an expert on something and has a pride to only use our language, we will keep it like that.
He's actually a chatter too.. we're discussed about many things in the past and we really have a nice conversation.. that's why he always told me to re-post his posts in english.
Well, he can keep with your language but also speaking or writing in English is broadening his horizon. That will certainly be a great way to grow.