Can someone confirm whether it is specified anywhere what the required standard is for the translation of a Manufacturer's Safety Data Sheet from Spanish into English- when I challenged it I was told it was an "error in translation"?

Regards

SDS’s should be in the customer’s language.
The problem of translation is that there are two approaches to the process- paraphrase, where you try to convey the meaning without necessary using the equivalent words- more useful I’d say and metaphrase which is a literal word for word translation which does not take into account idioms, words having multiple meanings etc.
There is a standard, EN 15038, for translation services but it does not describe in detail how to do a translation, just what quality checks you need to carry out.

If you can do that it would be better to buy from that supplier rather than the substandard one.
The MSDS is (should be) part of the "product".

Let's have level playing fields please