I don’t think Welsh nationalists are advocating for the exclusion of the English language in Wales. They are advocating for Welsh to remain the native tongue of the Welsh people.
That’s not what this article said.
“...The decision, voted through in January by Carmarthenshire council, will mean Llangennech school will join 479 others – just under a third (31.9%) of all schools in Wales – that teach exclusively in Welsh.”