Formal:
* Siarad Cymraeg (pronounced "see-ar-ad kum-rayg") - This is the most literal and formal way to say it.
* Siarad yn Gymraeg (pronounced "see-ar-ad un kum-rayg") - This is slightly more formal and emphasizes that the person is speaking *in* Welsh.
Informal:
* Siarad Cymraeg (pronounced "see-ar-ad kum-rayg") - The informal version is the same as the formal one.
* Siarad Cymraeg bach (pronounced "see-ar-ad kum-rayg bach") - This means "speak a little Welsh" and is more informal.
* Cymraeg (pronounced "kum-rayg") - This simply means "Welsh" and is understood to mean "speak Welsh" in context.
To ask someone if they speak Welsh:
* Ydych chi'n siarad Cymraeg? (pronounced "uh-duch kee 'n see-ar-ad kum-rayg?") - This is the most formal way to ask.
* Ydych chi'n siarad Cymraeg bach? (pronounced "uh-duch kee 'n see-ar-ad kum-rayg bach?") - This is a more informal way to ask.
It's worth noting that even if someone doesn't speak Welsh fluently, they might understand some of it.
It's also important to be respectful when asking someone if they speak Welsh. Be prepared to communicate in English if they don't speak Welsh.