Unfortunately we can't do that, as this would cause a real mess in the databank from
As you can see when having a look to the completed translations page, if you click to get on one of these pages, you will see (with flags from the languages that show on this page) into how many languages a text was translated.
I think the issue you're asking for would be something very difficult to implement. The webmaster will confirm with maybe more technical details than I'm able to provide you myself, I sent him a CC.
So it is rather the users who've got to adapt to the system than the opposite, I won't teach you that as you already know it.
One thing you can do is submitting a "A to B" translation request, then do the translation yourself into B. Then resume the same process from "A to C". Once these two translations validated by the experts, you will have the three versions you already know in our databank, and then you will be allowed to request a translation into this language D you don't know good enough.
The 3rd translation D will give the 4th version you are looking for, knowing this translation will possibly be obtained from A, B, or C.
I hope it helped.
Have a nice evening
JP, que penses-tu de la demande de notre ami a05?
CC: jp