It’s important to now I that Welsh miners were largely ignored not only by the Thatcher government but by the English-dominated miner’s union (NUM) as well.
I’ve asked that this thread be relocated to GD, Politics, or IMHO. It does not belong in Factual Questions because it starts right off with a leading question, making the assumption that the British government tried to oppress the Welsh language, just by how much. A factual question would be: Did the British government try to oppress the Welsh language? Even that is likely better in one of the other forums.
The fact that the British government tried to oppress the Welsh language is well documented. “Did the Thatcher government try to oppress the Welsh language” is less obvious. It is worth noting, however, that Thatcher reversed the government’s position to allow a Welsh-language television channel only under pressure of a hunger strike by a prominent Welsh-speaking politician, Gwynfor Evans: Gwynfor Evans | Welsh politics | The Guardian. The UK government certainly did not support and encourage Welsh the way they did English, even though both are official languages of the UK (Welsh only in Wales), and that disproportionate support over time certainly amounts to oppression.
For a long time Welsh was seen as a linguistic dead-end, something aspirational people wanted to liberate themselves from if they wanted to get on, rise in wealth, education and status. Teachers who suppressed the speaking of Welsh were doing their pupils a favour, as they saw it, by preparing them for the wider English-speaking world, something they would not be prepared for if it was always just a second language. Such attitudes were common around the world.
The coal mining areas were solidly Labour, always had been, and they weren’t going to vote Conservative ever, no much Thatcher tried to woo them. This is (was) the difference between British conservatism and US conservatism. If you are working class, you vote Labour. If you really can’t stand what Labour were currently doing, you voted Liberal (who were electorally negligible from the 1930s onwards). This picture began to change in the 1980s, partly because of the rise of regional nationalist parties.