"They were to blame."

Translation: Arnyn nhw roedd y bai.

[Not703679]

In the drop down information for the sentence duolingo gives: Arnyn nhw OEDD y bai, not, ROEDD y bai. Perhaps this difference needs explaining.

[Stephen996196]

And oedd y bai was accepted for me with no warning about a typo...

[iamOwenG]

The Welsh here is the emphatic form stating that it was 'they' that were to blame. I took the English to be the non-emphatic form. If it were emphatic in English, I would say "It is they who are to blame".

[dautofor]

while i agree that's technically correct, i feel it would be very peculiar to hear someone say "it is they who are to blame" in natural conversation. i would just put emphasis on the word "they" or say "blame THEM"

[iamOwenG]

I agree, but when you write it, there's no emphasis, so writing it emphatically makes it clearer. I think it's a distinction worth making so that it helps explain the Welsh construction.