If you look at Europe minus the former Soviet nations (ACEA figures in other words), then Japanese everyday brands are retreating. They are particularly being hit by Hyundai and Kia.
Below we see the difference, with Jan-Apr 2012 percentages first and April only figures in parentheses:
Mitsubishi -32% (-38)
Honda -22% (+2)
Suzuki -17% (-22)
Mazda -12% (-9)
Toyota -9% (-13)
Nissan -4% (-20)
Hyundai +9% (+0)
Kia +23% (+19)
There is nothing between the Korean and Japanese brands except value for money perhaps. I assume that is why the two Korean brands are taking sales from them, especially Kia. Honda showed signs of improving in April, and Nissan's poor April may just be an aberration. Premium brand Lexus is up 10.5% for the four month but down 39% in April, relying almost solely on the CT200H model proving unsustainable.
In summary: Japanese brands that make cars in Europe will fare alright, but brands such as Mitsubishi and Mazda will struggle. The new CX-5 will help the latter in the short term only. Offering value and more exciting cars is the way forward for Japanese makes. Then they will take sales back from the Koreans, who otherwise make pretty drab cars.