If you want to translate Magento extension, you have two options for that.
1. Please open app/locale/en_US/Module_Name.csv, copy it to your locale folder, for example to app/locale/de_DE/Module_Name.csv and change the wording after the "," so the line will look like "Product review","Testbericht".
2. Alternatively, you can use inline translation (provided the necessary language packs have been installed). Please go to admin/system/configuration/developer, choose the storeview you want to translate and enable inline translation for it. Then go to the front end, select text and translate it.