If you plan to optimize it for German language then promote it to various German based directories, sites etc
Optimization german website not differ from optimization anyone another website. links from websites in another language google will counter without problem. Of course, links from german websites is better.
Submit your website in German based directories & try to get local backlinks so it is easy to get ranked for your website
yes you have to promote your website in directory but for best promotion submit websites on German directory sites.
There are some .de directories and bookmarkings available on net. You can promote your site there. This will improve your rankings in google.de
I think he's asking in the sense that how he's going to do it (find good key phrases, write articles) without being fluent in German.
Do optimization first in English You can use the google translator for translating all the keywords and contents in english to german. Then, while offpage is considered, you can first go for german directories. You can also try german social networking, german forums (Search through google), german bookmarks etc try them and get back to us. Hope it helps.
Without proper knowledge of the language, grammar and semantics changing the on-site text is not recommend. You can however play with the tranlator for off site activities, i.e. articles on blogs for backlinks etc.
what is the content of your web page? if your web page is in german language it is best to target keywords in german as well as get quality backlinks from german sites.
Link building is the best way to take a quick promotion. In link building blog commenting is the best way to take quick link.