[hubert1234]

You say that somebody is wehmütig when he is purposefully trying to be sad and down on him or herself or everybody, so Wehmut is somewhat derogatory. If you tell somebody that they are wehmütig, it means that they are actively being dumb, basically. Melancholy is more like a wistful sadness also considered negative but connected to some tragic event or maybe when thinking about better times in the past a bit too much.