"Ffoniwch chi fi yn Gymraeg."

Translation: You will phone me in Welsh.

[Cynphony]

This sentence doesn't make sense to me at all. I can understand someone saying you will phone me in Wales or when I'm in Wales. I can understand "You will speak to me in Welsh.", but "you will phone me in Welsh" I don't understand.

[rmcode]

Yes, it is an odd sentence and would be better as a question, ie 'Will you phone me in Welsh?'

[DesertGlass]

I think that still has the same problem. To me the call is just the phone ringing. After that you can talk to them in Welsh

[rmcode]

Yes, this is a rather strange sentence, it's now been replaced with

"Faint o'r gloch ffoniwch chi?" = What time will you phone?

Thanks for the comment and pointing it out.