Duolingo not formal?
On duolingo it says ¨Sioned dych chi?¨ while on google translate it says ¨Ydych chi'n Sioned?¨. Why is that?
Google Translate's Welsh is just not very good yet. Nor does it draw a distinction between more formal and more colloquial forms of Welsh, so it is hit and miss what sort of Welsh, or what sort of mixture of registers, it will churn out as an attempted translation.
The usual form when asking people's names, jobs or relationships is an emphatic question - this means that the name is going to appear first in the sentence:
- Dewi dych chi? - Are you Dewi?
- Trydanwr dych chi? - Are you an electrician?
- Pennaeth yr adran ydy Dewi? - Is Dewi the head of the department?
(In more formal Welsh you might see an emphatic question starting Ai....? but you would be unlikely to hear it spoken. You may hear one starting Ife...? in some dialects, though. These words have no English equivalent; they are just particles which indicate the nature of the sentence they start - ['This is an emphatic question]...'.)
Because it's Google Translate. It's not always reliable, and it can use/prefer certain words over others. If you're going to use it, I would suggest using it for single words or to check sentences that you have written to see if it gets the point across that you are trying to make. =)