The preposition "yn"
I was told when "yn" means "in" it causes nasal mutation of the following noun, but I was doing a lesson and I was given the sentence "Dw i'n hoffi darllen yn Gymraeg" and it threw me off a bit. Is there soft mutation because it's an adverbial phrase? As in "I speak fast" or "I like reading in Welsh"? Would it ever be correct to say "Dw i'n hoffi darllen yng Nghymraeg"?
Edit: I had to post this here in the forum since I was doing the lesson on the mobile app.
Interesting question. That case had never occurred to me.
If you were saying "I live in Wales" you would definitely say "Dw i'n byw yng Nghymru" In your example Cymraeg is a language, and not a place, so the meaning of 'yn' is different. I'd go so far as to say it is actually a different word (but a homonym).
EDIT: One other possibility occurs to me. The correct full construction is actually "yn y Gymraeg" but the article 'y' is often left out. So the soft mutation is the residue of the article, and not due to the preposition 'yn'
Yes, your second point is the correct reason why it's Yn Gymraeg, strictly speaking languages are 'the Welsh' 'the English' etc in Welsh but 'the' has disappeared over time so 'Yn Y Gymraeg' has become 'Yn Gymraeg'.