I looked for one myself some time ago and couldn't find anything. The thing is that the SUS was released as a free “quick and dirty” scale and nobody “owns” it in the way the Human Factors Research Group at UCC controls the SUMI.
Perhaps more importantly, there are now quite some published data on the English-language version of the SUS and its characteristics that can help you plan and interpret usability tests with it (see references below). To my knowledge, nobody collected or published the same type of data for a German version. Short of that, there is really no telling how it compares to the English-language version and no strong basis to say that one translation is better than any other.
Depending on your needs and the amount of effort you are willing to put in this, you can do one of three things:
- Simply use a translation that feels good to you. It should certainly be enough to see some differences between designs or products, which is the most important way to interpret SUS ratings (absolute scores don't tell you much without a benchmark to compare them to).
- Go for the SUMI. It's a bit older and longer and isn't free but there is an official German translation and it will provide more information (it has several more specific subscales in addition to overall satisfaction/perceived usability). Wording of some of the items might sound awkward for some products, especially websites.
- Develop your own translation (and possibly publish it). The gold standard for this type of things is to have one or more experts translate the items from English to German and then other experts make a reverse translation to check if the meaning was not altered, revising the translations if needed. Then use this translation in a large user test (at least hundreds of participants and preferably different types of products as well), look at things like reliability and factor structure, compare them to publish data about the English-language version and check if some items have specific problems and need to be corrected or replaced.
Important papers about the English-language version of the SUS (beside the Brooke paper already mentioned):
- Bangor, A., Kortum, P.T., & Miller, J.T. (2008). An empirical evaluation of the system usability scale. International Journal of Human-Computer Interaction, 24 (6), 574-594.
- Borsci, S., Federici, S., & Lauriola, M. (2009). On the dimensionality of the System Usability Scale: A test of alternative measurement models. Cognitive Processing, 10 (3), 193-197.
- Lewis, J R & Sauro, J. (2009) The Factor Structure Of The System Usability Scale. Proceedings of the Human Computer Interaction International Conference (HCII 2009), San Diego CA, USA.
- Sauro, J. & Lewis J.R. (2011) When Designing Usability Questionnaires, Does It Hurt to Be Positive?. Proceedings of the Conference in Human Factors in Computing Systems (CHI 2011) Vancouver, BC, Canada.
- Tullis, T.S., & Stetson, J.N. (2004). A Comparison of Questionnaires for Assessing Website Usability. Proceedings of UPA Conference.
