When I "upgraded" to OSX 10.10 from 10.6 on my old Macbook Pro a few months ago, I discovered that the Dashboard Dictionary no longer had an English option. There was just Japanese, Greek and Russian. FYI, I have these 3 languages enabled in my keyboard input preferences, but English is the primary one. So, I assume that's how they ended up as dictionary options. But no English! After a bunch of tinkering but not remembering what I did, the English finally returned.
Now I just got a new Macbook Pro (with OSX 10.10.5), and have exactly the same problem again. I had installed all the files from a Time machine backup of my old computer onto my new one.
After much tinkering I'm still unable to get the English back. I tried deleting Japanese, Greek and Russian from the keyboard input options, leaving only English (Canadian English, to be precise). I think that's how I fixed it last time. But no luck this time.
I'm guessing there's a prefs or plist file somewhere that needs to be deleted, but I don't know where to look. Any ideas?