German language
The German language was a Human language spoken on Earth, predominantly spoken by Germans and in Germany, Austria, and Switzerland.

In the 19th century, a star chart of the inner part of the Sol system utilized the German language. (, opening credits)

German was the language used by the Nazi regime of the 20th century, both in the regular and in an alternate timeline. (; )

Ensign Hoshi Sato began speaking German while dreaming about her students back on Earth, and again later while attempting to break the lockout code in the decontamination chamber in 2154, while under the effects of a silicon-based virus. ()

In 2257 the universal translator onboard the  malfunctioned after receiving communications from a mysterious sphere.  This caused individual crew members and ship's computer to be heard in a large number of languages and for the ship's displays to switch to a wide variety of written languages. At one point, Captain Christopher Pike's speech was translated into German: "Töte die alarme. Was ist passiert?" ("Kill those alarms. Someone tell me what happened?") ()

Upon hearing Carl Jaeger's German name in 2267, Trelane asked him, in German, if he was a German soldier and reenacted part of a German marching song, singing, "Ein Deutsch soldat, nein? Ein, zwei, drei, vier, gehen wir mit dem Schießgewehr!". ("A German soldier, no? One, two, three, four, we go/walk with the rifle!") ()

The Nazi chant, "Sieg Heil!" ("Hail Victory"), was also spoken by a crowd of Ekosians in newsreel footage that was broadcast on Ekos in 2268. ()

"Wunderkind" was a German word meaning "wonderchild". Doctor Paul Stubbs referred to himself and to Wesley Crusher as a wunderkind in 2366. Wesley recognized the word as being German. ()

When a holographic  was conversing with Reginald Barclay after his intellect had been enhanced by the Cytherian probe in 2367, Einstein exclaimed, "Grüß Gott!" when Barclay showed him a revolutionary new way to look at the Theory of General Relativity. () 

A holographic representation of Sigmund Freud also spoke German, uttering, "Nein, nein, nein" ("No, no, no") when Jean-Luc Picard failed to grasp the meaning of one of Data's dreams in 2370. ()

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de:Deutsch
it:Lingua tedesca
Earth languages