What dialect of Welsh does the Duolingo course teach?
I'm considering starting it but I need to know if it will be compatible with my current learning materials.
Just start using Duo and see how you get on! Any variations you come across will be minor, and it is useful to be aware of them in any case, as you are bound to meet them sooner or later anyway.
The Duo course does not teach any particular dialect - there are about five main dialects, depending on how you define them, and there are large areas of geographical overlap in any case. The fundamentals of the language are the same across Wales. A few basic variations are introduced on the course, but that is as far as it goes. The computer-generated pronunciation is a pretty neutral one.
The course does not cover the formal registers of Welsh - the differences between that and colloquial Welsh are more significant than the differences in dialect.
If you live or regularly stay in Wales then it is a good idea to get along to some local courses where you will cover local variations and local pronunciation as well as the more widely used patterns that you will come across in the written and spoken media.
Which materials do you use?