Earlier quoted context omitted.
So in Scotland they speak Scottish-English? Irish-english in Ireland? What's your proficiency in these languages ?
I don't know about Scottish-English and Irish-English, to be honest. Would an English native understand them? Germans don't understand Swiss-German, and Swiss-Germans don't consider German as their mother tongue. Whereas the French being spoken on the French part of Switzerland is slightly different from the French from France, but people still consider that French is their mother tongue. Not sure if that answers you…
Depends where in Scotland and how much they've had to drink.
On a serious note, words like ken, bairn, breekies, stramash are not that well understood by English people. But it's unlikely a Scot would use them when talking to an Englishman.