What would the singular ("a Welsh speaker") be?
"Siaradwr Cymraeg" for a man, and "Siaradwraig Gymraeg" for a woman (note the mutation after the feminine form).
And remember that "Cymraeg/Gymraeg/Chymraeg" is always capitalised.
I wonder if someone out there can clear up a problem I have - which is “When do I translate’Cymraeg’ as Welsh language or just Welsh”
I think it's just a matter of whether the meaning is clear without the extra word. For example a "Welsh school" could be any school in Wales but a "Welsh speaker" would be taken to be a speaker of the Welsh language.