I have done Biology, Chemistry, Maths and German in AS. It really depends on you, for your GCSEs did revising for German take up a lot of time? Do you find German much easier than other subjects. German for me in GCSE was one of the easiest subject and I felt that it took the least effort for my AS, some people do seem to struggle at it for AS. I think it's nice to have a language next to all your science's and it isn't considered a 'soft' subject.