1957, from double (adj.) + speak, coined on model of doublethink in Orwell's "Nineteen Eighty-Four" (the language in that book was Newspeak).
Entries linking to doublespeak
double adj.
c. 1300, "twice as much or as large," also "repeated, occurring twice," also "of extra weight, thickness, size, or strength; of two layers," from Old French doble (10c.) "double, two-fold; two-faced, deceitful," from Latin duplus "twofold, twice as much," from duo "two" (from PIE root *dwo- "two") + -plus "more" (see -plus).
From early 14c. as "having a twofold character or relation," also "consisting of two in a set together; being a pair, coupled." From mid-14c. as "characterized by duplicity." The earliest recorded use in English is c. 1200, in double-feast "important Church festival."
Double-chinned is from late 14c.; double-jointed, of persons, is by 1828. Military double time (1833) originally was 130 steps per minute; double quick (adj.) "very quick, hurried" (1822) originally was military, "performed at double time."
The photographic double exposure is by 1872. The cinematic double feature is by 1916. Double figures "numbers that must be represented numerically by two figures" is by 1833. Double-vision is by 1714. Double indemnity in insurance is by 1832; double jeopardy is by 1817. The baseball double play is by 1866.
Double trouble "twice the trouble" is by 1520s; in 19c. America it was the name of a characteristic step of a rustic dance or breakdown, derived from slave dancing on plantations. A double-dip (n.) originally was an ice-cream cone made with two scoops (1936); the figurative sense is by 1940. Double bed "bed made to sleep two persons" is by 1779. Double life "a sustaining of two different characters in life" (typically one virtuous or respectable, the other not) is by 1888.
speak v.
Old English specan, variant of sprecan "to speak, utter words; make a speech; hold discourse (with others)" (class V strong verb; past tense spræc, past participle sprecen), from Proto-Germanic *sprekanan (source also of Old Saxon sprecan, Old Frisian spreka, Middle Dutch spreken, Old High German sprehhan, German sprechen "to speak," Old Norse spraki "rumor, report"), from PIE root *spreg- (1) "to speak," perhaps identical with PIE root *spreg- (2) "to strew," on notion of speech as a "scattering" of words.
The -r- began to drop out in Late West Saxon and was gone by mid-12c., perhaps from influence of Danish spage "crackle," also used in a slang sense of "speak" (compare crack (v.) in slang senses having to do with speech, such as wisecrack, cracker, all it's cracked up to be). Elsewhere, rare variant forms without -r- are found in Middle Dutch (speken), Old High German (spehhan), dialectal German (spächten "speak").
Not the primary word for "to speak" in Old English (the "Beowulf" author prefers maþelian, from mæþel "assembly, council," from root of metan "to meet;" compare Greek agoreuo "to speak, explain," originally "speak in the assembly," from agora "assembly").