"They speak English in England."
Translation:Labhraíonn siad Béarla i Sasana.
béarla (lower case b) just means speech, or even "mouth noise". béarla na n-éan - "birdsong", béarlagair - "jargon", francbhéarla - "lingua franca". It has just come to be used as the name for the English language.
Note that there is no connection between Gaeilge and Éire either.
Hmm, if I can find it fast enough, I can delete my comment on a very recent exercise introducing Sasana, which basically posed the same question. And yes, I did notice that Gaeilge and Éire are also not obviously related. I also wonder if béarla had some negative connotation when becoming the word for the English language, since I believe it is not uncommon to value foreign languages less than one's own mother tongue.