It's a German term that you rarely come across. It generally means.....someone or a political figure or a news media organization that is making or developing a story to be in a certain way.....to be interpreted by the public and create a particular vision by the reader or viewer.
The word has been around for than a hundred years....in case you think it's modern and part of modern TV journalism.
It got tossed around in July of 1914.....by various German newspapers....preparing the German for the upcoming war in August.
Stories were drafted to make the Russians sound "evil" on their intent to help protect Serbia. The French later were figured into stories.....labeling them as "evil" for helping the Russians. In a matter of days.....various stories were formed with a few facts and then have a few quotes thrown in to show a real person connected to the story.
How widespread was Stimmungsmacherei? Most all German newspapers were engaged in the activity during the summer of 1914.
Did it repeat in 1932? Yes.
Did it repeat again in the early 1960s with an anti-US dialog on the Vietnam war involvement? Yes.
Does it repeat today? Yes. You can watch the 8PM nightly news on state-run Channel One (ARD) and find the same type behavior.
The curious thing that they developed the practice over a hundred years ago, knew it was widespread, and generally have accepted the practice even today.