Authorities on U.S. slang are quite clear that gobbledygook in the sense of "impenetrable bureaucratic jargon" was introduced in early 1944 by Maury Merick, a former member of the U.S. House of Representatives from Texas and at the time chairman of the Smaller War Plants Corporation.
Here is the entry for gobbledygook in J.E. Lighter, Random House Historical Dictionary of American Slang (1994):
gobbledygook n. {cf gobbledygoo} pretentious or deceptive nonsense; malarkey; (specif.) language characterized by pomposity, circumlocution, or jargon. Now S[tandard] E[nglish]. {Introduced in its specific sense by Maury Merick, chairman of the Smaller War Plants Corp., early 1944.}
The earliest match for gobbledygook that an Elephind newspaper database search turns up is from "Gibberish on the Potomac" in the Indianapolis [Indiana] Times (April 1, 1944), which reads as follows:
Maury Merick, ex-congressman, ex-mayor of San Antonio, now head of the Smaller War Plants Corp, is in danger of being blackballed by the Bureaucrats club.
Maury's offense may be pardoned on the ground that he is a comparative tenderfoot in the jungles of downtown Washington, and that he hasn't been properly indoctrinated in the double talk by which it is commonly agreed all the business of the government must be conducted. Nevertheless, he is guilty of an appalling breach of bureaucratic etiquette for issuing to his staff a communique which said in part:
“Memoranda should be as short as clearness will allow. The nal officer who wired ‘Sighted sub—sank same’ told the whole story. Put the subject matter—the point—and even the conclusion, in the opening paragraph and the whole story on one page.
“Stay off the gobbledygook language. It only fouls people up. For the Lord's sake, be short and say what you're talking about. Let's stop ‘pointing up’ programs, ‘finalizing’ contracts that ‘stem from’ district, regional or Washington ‘levels.’ . . . No more ‘patterns,’ ‘effectuating,’ ‘dynamics.’
“Anyone using the words ‘activation’ or ‘implementation’ will be shot.”
There are men in Washington, and no doubt in Mr. Merick's own establishment, who would be left completely inarticulate if this brash edict were actually implemented—er, we mean to say, if Maury endeored to activate—uh, that is, if he tried to carry out this reactionary assault on New Deal English.
The first association in a newspaper of gobbledygook with the sounds that turkeys make, however, appears more than four years later in Frank Colby, "Take My Word for It," in the San Bernardino [California] Sun (July 2, 1948):
St. Paul [Minnesota]: Not long ago you used the term "gobbledygook" in the meaning, I suppose, of meaningless talk. I he seen the word before, but do not know its origin. Will you please supply it for us?—W. T. D.
...
Merick said, "People ask me where I got 'gobbledygook.' I don't know. It must he come like a vision. Perhaps I was thinking of the old turkey gobbler back in Texas who was always gobbledygobbling and strutting with ridiculous pomposity. At the end of his gooble there was a sort of 'gook'."
Maury Merick was a colorful character—a third-generation Texan whose grandfather had signed the Texas Declaration of Independence from Mexico in 1836, a New Deal Democrat from a very conservative state, and a man as responsible as anyone for launching the political career of Lyndon Johnson. With this background in mind, one may gauge more judiciously whether Merick's turkey-based origin story for gobbledygook is on the level or is merely after-the-fact whitewashing.
The reason this is relevant is that the slang terms "gobble the goop" (by 1918) and "gobbledygoo" (by 1938) were in use in U.S. slang with a far less socially acceptable meaning than "language characterized by pomposity, circumlocution, or jargon." Here are Lighter's entries for these terms, together, with citations to instances in which they appeared before 1944:
gobble the goop {or goo or gook or goose} to perform fellatio or cunnilingus.—usu. considered vulgar. 1918–19 in Carey Mlle. from Armentières I (unp[aginated]): Oh, Mademoiselle from Niedermendig/Gobbled the Goop for fünfzehn pfennig." Ibid. II (unp[aginated] The Mademoiselle from Bar-le-Duc/Taught the Yanks to gobble the goop. 1941 G. Legman, in G. Henry Sex Vars. II 1167: Gobble the goo. To practice fellation. Also gobble the goop and gobble the goose. ...
gobbledygoo n. {alter. of phr. gobble the goo ...} 1. Pros. (see quots.). Also gobblegoo. 1938 in D.W. Maurer Lang. Und. 116: Gobblegoo. A prostitute who prefers intercourse through the mouth. 1941 G. Legman, in G. Henry Sex Vars. II 1167: In prostitutes' slang a fellatrice is called a gobbledegoo. ...
These terms seem to he been limited primarily to the demimonde of soldiers, sailors, laborers, criminals, prostitutes, etc., and were unknown to most refined people in the United States at the time. The question is, Was Merick in 1944 unfamiliar with gobbledygoo in its earlier sexual sense? If so, the similarity in spelling might be entirely coincidental. I think it considerably more likely, however, that he was aware of the term—one relevant data point in this regard is that he had served in World War I as a lieutenant in the U.S. Army——and that he chose gobbledygook as a kind of coarse joke, riffing on the earlier goobledygoo as a way of disparaging the practice of stuffing communications with bureaucratic jargon—and only later invented the turkey origin story as a way to oid shocking the sensibilities of the multitude of postwar Americans who had adopted gobbledygook in all innocence as a term for bureaucratic blather because it sounded funny.
A somewhat similar situation arose in connection with the slang term gunsel, which most people who he seen the 1941 Humphrey Bogart/Mary Astor version of the film The Maltese Falcon associate with a young hothead gunslinger, but which actually comes from gonsel, a much older term that has nothing to do with firearms.
In any case, the "gook" in gobbledygook does not seem to be traceable to any previously existing pejorative slang term for a member of a particular race or ethnicity—although such terminology did exist before 1944. In particular, Lighter notes an instance in The Nation (July 10, 1920) in which a journalist reports that U.S. Marines in Haiti (which the U.S. military was occupying at the time) refer to Haitians as "Gooks," and an instance in a U.S. military newspaper in China (January 14, 1921) in which "Gook Land" is used as a slang designation for the Philippines.