The Glaswegian taxi driver may not consider themself to be speaking a different language but, if speaking to another local and leaving aside pronunciation, they’d use words, phrases and even grammar that’s incomprehensible to someone with no experience with Scots.
I’m a “posh Scot”, raised middle class in Edinburgh so my accent is minimal and thickens up or softens depending on who I’m speaking to. Even for me, there’s a lot of words, phrases and ways of speaking I’ve had to adjust to be consistently understood by American coworkers when over the last 10+ years.
Sort of like extreme cockney rhyming slang or for a more modern example thick BME* full of slang.
* = British Multicultural English, think fam n blud, lots of Jamaican english influence plus south east asian influence.
This is supremely ignorant. Scots is its own language. It's a 'brother' or 'sister' of English, with both English and Scots being descendants of West Germanic languages.
The fact that many (all?) Scots speakers also speak English doesn't mean Scots not a language on its own.
You could make your exact same arguments that Irish isn't a language because you could ask a Cork taxi driver whether he knows any English.
Scots = a language with some of the same ancestors as English.
Scottish English = a dialect (and accent) of English
Scots Gaelic = another language, with the same ancestors as Irish and Manx.
James Joyce wrote in English, no Irish person pretends that he wrote in a third language distinct from English and Irish. The fact that they do not do so does not compromise the political basis for independence, republicanism or reunification.
If a Cork taxi driver, addressed you in Irish (very unlikely), and you asked him to speak English, the request would be both coherent and reasonable. The point you missed is that the Glasgow taxi driver would look at you with consternation and say "But, I am speaking English! What's wrong with my English?' (insert dialect spelling if you like)
Rabbie Burns wrote in the same language as his compatriots Louis Stevenson and Scott.
It would be ignorant if I did not know about the meretricious claim of a minority of Scottish people to have their own language, but it is not ignorant to reject that claim. I am Scottish fwiw.
Geordie English is closer to Edinburgh 'Scots' than to RP English or US English or Indian English. Is it a dialect of Scots?
There exists dialects that are less mutually intelligible than apparently distinct languages, and the designation of each as "dialect" or "language" is political. Language is often a proxy for culture, and political actors may wish to suppress or boost the legitimacy of such cultural expression depending on their aims.