In this article we see a billboard whose most conspicuous feature is this word:
How is this to be understood?
Screenshot from the ad (source):
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The billboard is showing an advertisement for the Berliner newspaper Der Tagesspiegel. The full text reads
Wie das nach der Wahl alles zusammen funktionieren soll. Bei uns erfahren Sie es.
The text in smaller print could be translated as
How all that is supposed to work at the same time, after the election. At ours you'll learn it.
How all those topics are supposed to be addressed at the same time, after the election. In our newspaper you can learn about it.
So, the parts of the compound "Steuertemperaturmietensenkung" are actually meant to be incongrous. The ad plays with the German tendency to string along nouns into long and longer compounds. But these compounds seemingly don't work together at the same time - but the new government has to address all those problems at the same time. The ad invites you to buy the Tagesspiegel to read all about it ;)
Das Wort soll keinen Sinn ergeben. Die Zeile darunter lautet:
Wie das nach der Wahl alles zusammen funktionieren soll. Bei uns erfahren sie es.
Es wurden bewusst Wörter so aneinander gereiht, dass das Ergebnis keinen Sinn ergibt.
Der Tagesspiegel, von dem die Anzeige stammt, ist eine Berliner Tageszeitung.
The literal meaning of the compound word would be something like "reduction of the rent for tax (or steering/control) temperature" (or "reduction of the temperature rent for taxes"), which doesn't make any sense.
The word "Steuertemperaturmietensenkung" is likely meant to be understood as "Steuer-, Temperatur- und Mietensenkung" – "tax, temperature and rent reduction".
The three German parties which are currently negotiating after the election to form the next government (SPD, Greens, FDP) each have a main goal they want to have addressed:
(To many, including the author of the billboard's message, this seems to be impossible to finance all at once.)