You can compare multiple copies in multiple languages for consistency. Much the way you'd look for multiple written records of an ancient battle to see if they aligned. The scriptures are remarkably consistent and any discrepancies are typically either easy to sus out (such as fabricating a section about the trinity), or one off references to a Hebrew word where the translation is murky and easy to handle. E.g. there's a section about not eating certain animals that has a one off reference to an indeterminate bird. Could be an ostrich, or an owl, or some other type of rock-dwelling predatory bird. While no one's entirely certain exactly what that one-off bird is...it's pretty easy to just not eat those birds since you're not going to eat them anyway.