First I obsessively translated Hachi's Twitter. Then I decided to branch out a little.
If you're looking for OSTER project's Twitter, it's here now.
This page is an archive at this point; I've stopped translating all of these, and the ones marked "retired" I stopped doing even earlier than that due to them not doing Vocaloid/becoming inactive/etc.
Den (@denugrw) (Retired)
Furukawa (@fullkawa_honpo) (Retired)
mayuko (@mayuko_pink) (Retired)
papiyon (@papiyon_cyoucyo) (Retired)
Task (@task_plus9) (Retired)
wowaka (@wowaka) (Retired)