It was in Welsh and called Y Gywll when it aired on S4C last year, but now, thanks to my suggestion at the BAFTA preview (no doubt), it’s on BBC Wales in both English and Wales. Compare and contrast:
The bilinguality is handled quite well and adds a new element to the show, although you can spot the joins if you look hard. Mattias is now the English-speaker in a community of Welsh-speakers. The other cops all speak Welsh and purely through the editing, there’s an element of him seeming to force them to ‘behave’ and speak English. But since a lot of the locals speak Welsh, Mattias finds he has to rely on the others to question those who either can’t speak English or won’t, or who won’t confide in him, only in a local. There’s not a lot of Welsh in it but there’s more than zero.
Episode 1 was on Saturday, but you can watch it on the iPlayer if you missed it. No word yet on its BBC4 air date and what languages it’ll be in on that channel, though.