The forms of Welsh covered on this course are not 'wrong'. They follow the forms taught on the national DysguCymraeg courses for adults in Wales.
There are about five main dialect areas in Wales as well as a range of registers from the casual or slang forms up to very literary forms now rarely used. This course covers only a very few dialect variations, and it sticks to a middling, colloquial register that will form a basis for learning other registers of Welsh.
Where British English patterns in the translations can be confused with other patterns, we stick with the usual British usage.