In American English we might say " I go to Brecon tomorrow." Why is that not correct here?
Yep same in uk english, in fact when I learn french here they make no distinction between verbs 'i do' and 'im doing', so I thought it would be the same yn gwmraeg
I've never heard this sort of expression translated as 'I go to <place> tomorrow'; only 'I am going to <place> tomorrow.
Generally the philosophy we have is that we will add any vouched for English translation since we are not teaching English and there are so many world wide variations of grammar, spelling and idiom.
However in this case we're going to need a link to this phrase being used in this way.
We're happy to add it if such a reference exists.
Im pretty certain there are many of examples of "go" being interchangable between present and future, although that might just be slang. 'i go to brecon tomorrow' is the same as saying 'i leave for brecon tomorrow' but perhaps because 'leave' can be interchangeable as opposed to 'I am leaving', then some people assume 'go' can be used the same way. The word 'leave' doesnt change between present and future, because 'i am leaving' could mean 'i am currently leaving' or 'i am leaving in an hour'. Likewise, other verbs could be used the same way.
'I am going...' - with the same range of possible meaning as in English, really, leaving the 'tomorrow' to indicate the future rather than the present.
Bydda i'n mynd... - 'I will go/be going...' - definitely in the future