Generally it makes no sense to use any other language than English for comments (unless it's some small inside project ). For example, my native language is Finnish and there wouldn't be many programmer around who actually could read those comments if written in such rare language. Therefore I'm wondering, why they used German language in first place.
It really doesn't seem like portability should be a huge goal for writing code for top-100 supercomputers.
It depends on what are you doing. If you have relatively short term project (say less than couple of years) you are right. But if you do some serious long term research, portability comes with huge impact. Especially if your project has relatively large code base. Thing is, architectures comes and goes and you can't count what architecture you are going to use five years from now. Another thing is that you might use wide variety of computing sites, when portability is essential, really.