A favourite imaginary textbook is Farthing's This Bees Speech, invented by Anthony Boucher for his 1942 story "Barrier". Five hundred years in the future, the English language has been tidied by the ultimate nanny-state. Irregular verbs are forbidden, and thus "is" gets simplified to "bees", while "was" and "were" become "beed". Farthing also declares that "Article bees prime corrupter of human thinking" – so goodbye to "a" and "the". You get sentences like "they prohibited all drinking because drinking makes you think world bees better than it really bees ..."
Douglas Adams went in the opposite direction with ever more complicated verbs for time travellers who need to use the Future Semi-Conditionally Modified Subinverted Plagal Past Subjunctive Intentional, and understand that the Restaurant at the End of the Universe isn't a place which is but which wioll haven be.
In Robert Heinlein's The Moon is a Harsh Mistress the Russian-descended narrator follows Farthing in being anti-article: "Human brain has around ten-to-the-tenth neurons." Strangely, the non-Russian girl genius of David Palmer's novel Emergence uses the same shorthand ("took best part of three hours to complete crossing"), for absolutely no logical reason except homage to Heinlein.
What used to get writers really worked up was the dread prospect of spelling reform. The non-hero poet of "Enoch Soames" by Max Beerbohm time-travels from 1897 to the British Library of 1997 to find what posterity thinks of his poems, and discovers in Inglish Littracher 1890-1900 that he's known only as a fictional character in Beerbohm's "sumwot labud sattire". Beerbohm, telling the story, claims that he's never managed to decipher "labud".
Such phonetic language turns up in various SF novels that scare off lazy readers, like Russell Hoban's Riddley Walker (told in future Kentish dialect) and Iain Banks's Feersum Endjinn – where a whole story strand is narrated by young Bascule the Dyslexic, so u ½ 2 reed ded slo 4 thi ritin 2 mayk eni sens @ orl ...
Which reminds me that the oft-reprinted joke essay "Meihem in ce Klasrum" by Dolton Edwards, which takes phonetic English to bizarre extremes, first appeared in Astounding Science Fiction. So it must be SF! Edwards imagines a glorious future containing "no mor uv ces teribli trublsum difikultis, wic no tu leters usd to indikeit ce seim nois, and laikwais no tu noises riten wic ce seim leter ..." Max Beerbohm would have had a fit.
When characters "hier" and "spiek" dialogue in Cordwainer Smith's Norstrilia, though, this isn't language reform but special terminology for hearing and speaking by telepathy.
In 1984, George Orwell famously imagined a revision of English that would underpin the totalitarian state by making it impossible to express subversive thoughts or "crimethink". There are some interesting SF riffs on the idea that language shapes our thinking. Social engineers in Jack Vance's The Languages of Pao force three designer dialects on the placid folk of Pao in order to create castes of warriors, technologists and salesmen. Suzette Haden Elgin, feeling that languages largely invented by men have a chauvinist if not outright violent bias, offered the alternative women's language Láadan in her Native Tongue. Thinking in the alien tongue of Samuel R Delany's Babel-17 has the reverse-Orwell effect of programming you to become a fifth-column saboteur. And Gene Wolfe's The Book of the New Sun outdoes Orwell with a whole country – far-future North America – whose citizens speak only in preset political slogans from a little red book. Somehow they still get their meaning across. Wolfe includes an entire story told in this jargon by a character whose name comes from the same book: Loyal to the Group of Seventeen.
The late great Robert Sheckley went further in a story called "Shall We Have a Little Talk?", featuring a language that evolves so very fast that the hapless linguist from Earth (who wants to exploit the natives) is unable to cope. He finally gives up when the lingo mutates into endless different intonations of the single word mun. A native elder speaks the punchline: "'Mun-mun-mun; mun, mun-mun.' This was, ironically enough, the marvellous and frightening truth of the situation ..."
Fortunately, the English language of the real world is nothing like these strange fancies of SF authors. We all know about broadband, blogs, vlogs, chicklit, podcasts, malware, WMD, carbon footprints, tasers and scrotties. (Well, all right, maybe not scrotties – which years ago I made up for a story, as the name of the next big thing). We didn't have to struggle, like Sheckley's linguist, to keep up. We are the natives and secretly we're pretty sure we've known these terms all our lives.
David Langford is aware that the gostak distims the doshes.