Back on October 1st, Nicovideo announced that they would be updating the site to support English visitors. This change comes at the same time as Nicovideo’s full transition to their new “Niconico Zero” interface.
Go ahead and check it out for yourself. This will certainly make site usage and navigation much easier for Vocaloid fans.
EDIT: Please make sure that you are registered on either niconico.com or nicovideo.jp. Then change the language setting at the bottom of the page.