The landmark writer's guide The Elements of Style states that you should "not be tempted by a twenty-dollar word when there is a ten-center handy, ready, and able." German, however, has quite a number of words that "are so long that they have a perspective," as Mark Twain once wrote. The longest word actually included in the Duden German dictionary is die Kraftfahrzeug-Haftpflichtversicherung (auto liability insurance), with 35 letters. There are, however, many longer words that are acceptable to use although not listed in Duden, such as die Verkehrsinfrastrukturfinanzierungsgesellschaft (traffic infrastructure financing society) and das Elektrizitätswirtschaftsorganisationsgesetz (electricity economy organization law). Such "20 euro" words are not only found in written German, but also in spoken German, as evidenced by these Yabla German videos!
Auf Weltmeisterschaftsebene
At World Cup level,
sind wir so Mittelfeld, unteres Mittelfeld...
we are about midfield, lower midfield...
Caption 70, Frisbee - Karlsruher Weihnachtsturnier
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Außerdem kann man hierzulande
In addition, in this country you can
manche Reisestrecke auch ohne Geschwindigkeitsbegrenzung erfahren.
also experience some travel routes without a speed limit.
Captions 22-23, Reiseland Deutschland - Vielfalt im Herzen Europas
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Wir haben die gesetzliche Verpflichtung,
We have the legal obligation
regelmäßig die Geschwindigkeitsbeschränkungen auf den hessischen Autobahnen zu überprüfen.
to check the speed limits on the Hessian autobahns regularly.
Captions 10-11, Deutsche Autobahnen - Geschwindigkeitsbegrenzungen
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Ein Porsche dreihundertsechsundfünfzig B eintausendsechshundert GS
A Porsche three hundred fifty-six B one thousand six hundred GS
Carrera GTL Coupé, Baujahr neunzehnhundertsechzig mit Note eins hat somit laut Classic Data
Carrera GTL coupé, built in nineteen hundred sixty with a grade of one, according to Classic Data
einen Versicherungswert von sechshundertfünfzigtausend Euro.
has an insurance value of six hundred and fifty thousand euros.
Captions 57-59, Porsche 356 - Der erste Porsche
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So as you can see, in common conversation about sports and cars and numbers (or a combination thereof), it is possible to find some "mouthfuls" indeed.
Further Learning
Read some of these fun articles about long German words at The Week and Time, and if you are feeling brave, read this Duden article about writing words together or separately.