As a collector of the official Touhou games (the goal is to have all main games and spinoffs including PC-98...eventually), I'm not sure where I could find a translation for one thing in particular: the cover of the game. Specifically, the back cover of the jewel case.
To some this might seem trivial, but for me it's fascinating to see how ZUN would try and sell the game with the flavor text on the back of the case.
I'm wondering why they haven't been translated, my best guess being how the actual covers are hard to come by due to a limited (?) release of pictures of the game case itself online. Either that or I am looking in the very wrong place, please correct me if I'm wrong.
It also may be interesting to those interested in the images of the games (especially earlier games) before they released, with a potential for beta screenshots. Though I haven't personally noticed too many differences.
Now I don't have nearly all of the games yet. (I'm too low on money :V ) I can provide high quality pictures of the back covers themselves if this hasn't been done and if someone is up to the task. As of 6/13/17, I have EoSD, IN, PoFV, and ULiL. I'm not sure if this kind of thing will take off and be interesting to people other than me, but I'm more curious than anything.