The story that's been told is that his English speaking bosses wanted him to speak English in the kitchen. He refused, speaking Welsh to the Welsh speakers and English to the English speakers.
They sacked him, claiming it had nothing to do with the language.
A tribunal found that it was about his use of language.
> If he was Russian or Chinese and nobody could understand him in either English or Welsh, I don't think it would legally be discrimination to fire him (nor morally).
I'd be interested to know what would have happened if it had been a language other than Welsh.
If there were a bunch of people who spoke Russian fluently, and he spoke Russian to them and English to the English speakers.
So in multilingual jurisdictions there can be strong employment protections around speaking one's choice of national language. In this case the article says there was the Welsh Language Act of 1993, which presumably says that citizens of Wales are free to conduct all of their business in English or Welsh and shall not be discriminated against in any professional or government capacity for speaking either language as they please.
It's about workplace expectations that derive from the local culture. The hypothetical comparison that comes to mind would be if California adopted Spanish as a second language or something.
If he was Russian or Chinese and nobody could understand him in either English or Welsh, I don't think it would legally be discrimination to fire him (nor morally).