...in which Pembrish is spoken in Wales, which is ruled by Scotland; the Vikings speak an Ingvaeonic language; and Mercia remains independent from the rest of Britain, and ruled by the French.
There are three points of divergence. First: the Saxons expand north into western Scandinavia; second, speakers of the West Saxon dialect of Old English expand into Wales to escape the Norman Conquest; third, the Tangut Empire does not collapse into incompetence, but instead expands under Renghis
and his successor, bringing the Black Death to Europe about a hundred years earlier.
Ingvaeonic dominance of western Scandinavia creates closer ties to Scotland (which here means the Germanic-speaking part of Britain, distinct from Mercia, the Romance-speaking part), leading to its eventual entry into the Kalmar Union, which is not an alliance against the Germans but a mutual defense treaty between the Saxons and the Scots preventing northward expansion by both the Germans and the Mercians. Similarly, France retains closer ties to Mercia.
I am not really sure what happens after that. The Middle Ages are hard.
But, to guess: Mercia becomes a merchant state, with London taking on the same role it does today. Belgium may or may not exist, but Mercia gets the Congo. The advance of the disorder brought on by the Black Death means that the Spanish don't get to North America right after the collapse of the civilizations there. They take a few islands and then get their asses kicked, but New World diseases probably still spread. France might take South America; I'm not sure how different North America would be, since it would probably be claimed by Scotland and settled mostly by Irish and Germans. The War of Secession might become a proxy war between Scotland and France/Mercia; whatever happens, the Confederacy, of course, wins.
Assuming the World Wars still happen roughly as they did in our timeline (and I don't think Eastern Europe would look all that different), something something Manchuria. The Treaty of Versailles (assuming ~WWI doesn't go differently, but I'm not sure what North America would look like yet — that is, who's in the Union and who's in the Confederacy) would be complicated by Mercian merchant pillaging, which would probably piss off Germany even more, whatever Germany ends up looking like.
Absence of England means absence of English philosophy, which means the empires probably do not blow up as easily as they did in our timeline, and the early-20th-century left looks very different. I am not sure what consequences this would have.