I guess that you're talking about China and Japan talking openly about supporting the Europe. So, it may due with various reasons.
I guess for many year, the main trading partner of both China and Japan are the US. Now both countries are facing tremendous pressure in appreciating their currencies; therefore, they must looking to buy other currency as a way to devalue theirs. Besides the US, Europe is surely a next big trading partner, therefore, both Japan and China would want to support the currency as much as they can. Not only it's good for their economy but it also help to stabilize the world economy. By buying bonds issue by their European country, both China and Japan had done several good things.
First, Support the Europe from falling lower while lower their own currency. The higher Europe would support their export products.
Second, diversify their holding from too much reliance on the green back.
I guess I can talk more about that, but don't know whether I'm talking about what you want to discuss/ask.
Anyway, I also hope to hear other people ideas.