What do you call faking to speak a foreign language?

You can watch examples of this in the following Danny Kaye video that compiles scenes from several of his movies:

Fan Tribute - Danny Kaye: Master of Many Many Tongues...Indeed

Or in Chaplin's "The Great Dictator" too:

The Great Dictator - Fake German Speech Scene (No "Translations")

In short, it's all about mimicking intonation, sounds, even gestures of the foreign speakers, as perceived to the speakers of your own language, just to give the impression that you're actually speaking the foreign one.

I think it's mainly used in humor:

Italian interpreter?

Is there a term (verb or noun) for this gibberish just to fake you speak a foreign language? Is this a rhetorical figure with a name?

• This scene is an example of an improvised [rh.fig.] by Charles Chaplin.

Or may be there exists a verb:

• Danny Kaye usually [verb]s in his movies.

Solution 1:

https://en.wikipedia.org/wiki/Double-talk

Double-talk is a form of speech in which inappropriate, invented, or nonsense words are used to give the appearance of knowledge and so confuse or amuse the audience.

Comedians who have used this as part of their act include Al Kelly,1 Cliff Nazarro,[2] Danny Kaye,[3] Gary Owens, Irwin Corey,[4] Jackie Gleason, Jerry Lewis, Sid Caesar,[5] Stanley Unwin,[2] Reggie Watts,[6] and Vanessa Bayer. [7]

https://grammarist.com/interesting-words/doublethink-doublespeak-or-double-talk/

Double-talk means speech that is impossible to understand, usually a mixture of purposefully unintelligible words and random, nonsense syllables. Double-talk is used for humorous effect, usually to mimic a foreign language. However, the term double-talk make also be used to describe speech that is used to confuse people, somewhat similar to the meaning of doublespeak. Note that the proper spelling of double-talk is with a hyphen, though it may be spelled as two words as in double talk, or the two words may be melded together as in doubletalk. The word double-talk was first used in the 1930s.

How Sid Caesar Learned Double-Talk

By BEN ZIMMER

The obituaries for the great comic Sid Caesar invariably mention his proficiency in “double-talk,” mimicking the sounds (but not the sense) of foreign languages. It turns out that this was a talent Caesar had cultivated ever since he was a boy clearing tables at his father’s restaurant in multi-ethnic Yonkers.

The New York Times:

He could seem eloquent even when his words were total gibberish: Among his gifts was the ability to mimic the sounds and cadences of foreign languages he didn’t actually speak. Reuters:

Some of Caesar’s most popular bits were built around pompous or outlandish characters—such as Professor von Votsisnehm—in which he spoke in a thick accent or mimicked foreign languages in comic but convincing gibberish.

“He was the ultimate, he was the very best sketch artist and comedian that ever existed,” [Carl] Reiner said of his friend. “His ability to double talk every language known to man was impeccable.”