The same applies to translation offers we received for versions in Dutch and Japanese, for example.
This is why:
VTrain is being reformed all the time in both coding and documentation. Often the changes are very slight, and each one of them must be implemented into each of the three versions. (BTW This is tiring, unrewarding work, especially if you are a bloody perfectionist and the slightest chance of improvement that comes to your mind is taken into action at once.)
Neither keeping track of the modifications nor re-translating the whole thing prior to each release is affordable for a project such as VTrain that is not essentially a for-profit venture.
Now, you may argue that many other applications limit their translations to the resource files (menus, dialog boxes, etc.), excluding the documentation. But considering the relatively steep learning curve of VTrain, this would not be enough. And anyway, someone who understands the Tutorial in English is likely to be able to handle menus and dialog boxes in English as well.