I want to see that rule being applied, I am sure the other European countries are not gonna like it. Can't imagine this taking place... Even if, there will be ways to pass a language test (and if it by learning the language).
Anyway, you never know how things might change, BUT all ops and procedures are supervised by the LH mainline safety pilot and the German pilot union (or its counterparts in the company). Therefore I do not see, why the 42 months/3000 hrs rule should/can be changed. Until now, LH was a company that you stayed with for your whole life! Nobody normally made it under 10 years from the right to the left seat and once structures at LHI are established, I can imagine that things might be similar. So if you want to become captain in the fast line, sit in the right seat for a short while now or go elsewhere. That will propably be your only chance with LHI for some time.