While 'dw i'n dod o Sbaen' could be correctly translated as either 'I come from Spain' or 'I am coming from Spain' the addition of 'yn wreiddiol' makes the second sentence, ie your suggestion, grammatically incorrect in English.
Since 'originally' implies one single completed journey, while 'I am coming' is a journey either being undertaken now or in the future.
Oh, I thought it just means "I am originating from some place" rather than "I'm going from some location"
Here are the current correct translated for the sentence:-
I originally come from Spain.
Originally I come from Spain.
I am from Spain originally.
I'm from Spain originally.
I come originally from Spain.
I am originally from Spain.
I'm originally from Spain.
I come from Spain originally.
But if you think your suggestion has a similar meaning then I'm happy to add it as this is not a course to teach English grammar. OK that's done now.
It is just awkward English, really. 'I'm coming...' is a present progressive verb, whereas '...originally' points to a past action - the two don't go well together.
If you look at an English language textbook such as the Longman Student Grammar you will probably find detailed examples and explanations of verb aspect.
I‘not the one to judge, because I'm a non-native speaker, but I'm sure I caught this bad habit here on duolingo, in many courses (Swedish and German come to mind) this expression is used in the same context.