If anyone is interested, Mangagamer finally did listen to the suggestions and
started offering demos.
One of the current three games available with a translated demo is
Kira Kira (demo is mirrored
here ). The demo contains quite a lot in my opinion. Basically the whole school chapter phase is playable with it, and there are a many funny moments in that part.
Please try it out now if you have some free time. After playing through I have to say it is indeed a great game and the demo should be able to reflect that.