Is that literally true? I would have expected Germans to rate their bridges in tons, not pounds/pfund.
What I don't understand is your claim that "you could just as well consider them metric tons". These are short tons with caveats, i.e. the eventual number depends on more than just the raw weight, but the raw weight is one aspect of the calculation.
So if you were to make that calculation on the basis of metric instead of lbs how aren't you going to introduce something like a 10% error in the MLC you come up with?