People often have reasons to communicate to trusted others without being overheard. Aristocrats had a private language if they did not want to be understood by servants: “pas devant” signalled a switch to French. “Ag-ag” was spoken by grandmother when she was in service in late Victorian times. Being overheard complaining about the lady of the house might result in dismissal. Girls would insert an extra syllable if speaking about the mistress of the house: “thagis agold kaygat” became “this old cat”.
Polari
Polari was a a small number of dialect words mostly concerning illegal sex, either gay or sex work. It appeared to come from Mediterranean seaports, but was also used for Punch and Judy in fairgrounds.
Rhyming slang
Cockney rhyming slang probably developed around illegal horse race betting to reduce the risk of being overheard by a policeman.
Widely recognised Cockney slang terms for money show their origins in illegal betting, including ‘pony’ – £25, a ‘ton’ – £100 and a ‘monkey’ – £500.
“Use your loaf” – loaf of bread, “head”, and “mince pies – “eyes” are now widespread.
Glottal stop
Closing the focal folds in English serves as an alternative (allophone) to “t”, but to some extent to the other five stops. It is written /ʔ/ in IPA.
Long regarded as a feature of the Cockney accent, recently it has spread to a wider area of London and Essex and called “estuary”. It is now being reported in the speech of Leeds, Dundee, Prince Harry and the TV presenter Lorraine Kelly. The English linguist David Crystal reported it back in the 90s, but he not know what drives it. If its use continues to expand, glottalisation might replace most stop consonants and make English incomprehensible to foreigners. This might be a clue. What if the motive for its use is to make it difficult for outsiders to eavesdrop on in-group speech, as rhyming slang was?
leʔs go ʔa thə doʔ ‘n duʔ n aʔ ə cuʔəl ə pinʔs ‘n steaʔ n pəʔaʔəs
(let’s go down to the Dog and Duck and have a couple of pints and steak and potatoes)
It is possible to replace not only “t”, but also “d”, “k”, “g”, “p” and “b”. The sentence above suggests that /cuʔəl/ might replace “couple”. Has any reader heard this? Replacement is most difficult in the onset of a syllable, but easy in nucleus and coda positions.
Is the purpose to become less comprehensible to second-language speakers? If the privacy hypothesis is correct, glottalisation might be an optional code switch. English would certainly become much harder to understand if our six work horse stop consonants were frequently replaced.
The Chinese Alpaca campaign
The grass-mud-horse was a Chinese internet campaign in 2009 using an Alpaca image.
DNA code
is having some transfer into common speech. A genome is listed as codons which are groups of three letters selected from an alphabet of four – A,C,G,T. A 3-letter codon defines an amino acid, which makes an enzyme, which makes a protein. https://en.wikipedia.org/wiki/DNA_and_RNA_codon_tables
Alphanumerics have been given arbitrary associations with codons, allowing “boiler plate”. Here is the graphic for decoding your name from DNA code. There is translation engine here. https://earthsciweb.org/js/bio/dna-writer/
DNA code became suddenly sharply relevant on 3 Feb 2020 when Prof Zhang of Shanghai published the complete sequence of COVID-19. Microbiologists around the world were able to start designing a vaccine the same day.
Morse code
Telegraphs in the 19th century used patterns of short and long clicks to represent the letters of the English alphabet and the numbers 1 to 0.
The bandwidth was low. A ham operator had to be able to transmit 20 words per minute to get a licence. There were hundreds of abbreviations made up a few letters. <R> meant “correctly received” and became “Roger”; <WC> meant “will comply”. Hams had their own slang: <75> meant “inexperienced operator”, one who might use the poor quality 75-meter band.
Telegraphers of other languages had to find ways of spelling their language in this very sparse character set. For example, the German <ö> in Österreich had to be written <oe>. In World War Two German and Japanese Morse was using the same character set. The German Enigma code provided a way of coding letters. Bletchley Park had to to try millions of possible combinations but Turing realised that human fallibility meant there was more regularity than the code-designer intended. Every message was likely to include the six-letter group <HITLER> and a lazy operator might choose <BERLIN> for the encryption key.