temptress (plural temptresses) 1  An alluring woman who seduces or exploits men. 2  A woman considered sexually attractive by men. Marilyn Monroe, the iconic temptress of the 20th century.
Sarcasm is difficult to understand when crossing any language barrier, but yes it is a popular stereotype that the Germans have little sense of humour. I work with several german clients and they don't put up with anything let's put it that way. Just Google it.
Ich liebe dich is the most common way to say it. It's also important to learn the other German love phrases on this page as well. For example, if you would say I love you and the recipient would say kiss me. If you didn't understand the other person, that could be an opportunity lost.