"D'fhás an gairdín go mall."
Translation:The garden grew slowly.
This pronounciation bears no resemblance to what I learned in school, is it dialectical or should it be reported?
The pronunciation of 'mall' is correct, at least in some dialect(s). You're right about the 'd'.
The current (native) speaker doesn't use a particularly slender "d" in "gáirdín" either.
I heard a perfectly normal slender d. Unless you're expecting the full-on Donegal 'j' for it.
And the original speaker no doubt had a perfectly normal Munster pronunciation of a slender "d".