Unable to change theme's font

HI, I really love your theme. I’m developing a bilingual website, when I change it into Vietnamese, it can’t display well, even worse when I suft by mobile service. I try to change every “Roboto” into Times New Roman in theme’s files(template.css,editor-style.css), delete everything in folder “font” and when I checked again, it’s still Roboto.
my website is: https://www.turnthingson.com