Wikipedia shines here. The German entry for Konstrukteur correctly provides a link to the English site’s design engineer page. The only slight problem is that these two terms only correspond for mechanical engineering. German electrical or electronic design engineers usually use Dipl. Ing. Elektrotechnik / Elektronik to fill out their business cards. See Berufsbezeichnungen. Note that Germans have adopted Design as a German word, but they currently consider it to be exclusively arty-farty. Should you get an interview as a designer at Siemens they won’t be asking you about characteristic impedance, but they may well ask what you think of Shiro Kuramata.