How does anyone know if story cycles and legends - which generally seem to be medieval, no earlier - can tell us anything much about belief systems that existed prior to Christian, medieval Europe? Aren't they refracted and distorted through the Christian lens? Rely on these texts is dangerous, surely?
There is also a problem with people basing their lives/belief systems on anything for which they have to rely on translation.
One reason to be a pagan is to reject living by any book or dogma. Sure, it's a way of life for others who can't break away from the lure of dogma, being told what to think by a written text or a liturgy. But for others, it has no authority.
I love "The Mabinogion" but I could never live by it, quite apart from the fact I can only ever read it in translation so can only pick up a shadow of what it's actually saying.
Linguists are still making inroads into unravelling the texts, allowing us to see the influences, so I don't consider an inability to read texts in their original language a barrier. Besides which, I don't have the ability to read any of the texts in their original language, nor do I have the means to go to university and study linguistics, history and archaeology in order to confirm/deny for myself the validity of the translations. Then again, I suspect I'm not the only pagan in this position. I imagine a lot of heathens, celtic and brythonic pagans find themselves in the same position. I suppose western buddhists and other non-Christian groups would find themselves with similar dilemnas.