That was not the root of the problem. It seems that as soon as I edit a bone in blender (rotation or translation) this will ultimately also be applied to the animation and therefore distort it. I just created a whole new skeleton from scratch that matches the UE4-Skeleton regarding the bone hierarchy but even with that the animations are completely distorted… However, if I import the standard UE4 Character and just take his armature, don’t edit it and apply that to my mesh (also it doesn’t fit) the animations play fine upon importing it in the editor (the weight’s of course don’t fit, but the bones aren’t off…).
Maybe I’m doing something fundamentaly wrong but I have now idea what that might be