I think it should start like this: "Though the rhetorical theories that follow are often labeled ..." Here is what I think it means: Though the persuasive language ideas here are often labeled as "British," most of the people who came up with them are Scottish and one is Irish. British does not always mean English when the term is used to talk about eighteenth century language ideas. You should be aware that England, Scotland and Ireland are all separate countries. I hope that is helpful!!!

Through the rhetorical theories that follow are often labeled "British," most of the thinkers described are Scottish, and one Irish. British should not be taken to mean English when applied to eighteen-century rhetorical theory. "Even the rhetorical theories that follow are often described as if they were "british", most of the thinkers described on it are Scottish, and one of then is Irish. The nationality "British" should not be understood instead "English" when we are studying rhetorical theories of the eighteen-century." Hope it helps you. =D

I think you mean to say "Although the rhetorical theories that follow are often labeled "British," most of the thinkers described are Scottish, and one Irish. British should not be taken to mean English when applied to eighteen-century rhetorical theory.". Is it the geographical/historical issues you don't understand, or the language ones? To address the former, the Kingdom of Great Britain in the eighteenth century included both Scotland and England, as well as Wales. (Great Britain is the island which is shared between those three countries, and "British" refers to that land as a whole.) But Ireland at that time shared the same kings, so it was brought within the same sphere of influence. However, technically, the Scots for most of the 18th century were British, but the Irish were not. (They became so in the 19th century.) The English were at all times considered British, but the reverse is not true. It is still the case today that "English" should not be confused with "British". When the author says "British should not be taken to mean English", that is what they mean.