Well, the lore of the books was that they were scattered after the war. That is, they existed before X became god of secrets, and before the gods were divided as good or evil. The books themselves could be written by Hal and Darko, yet this would be a highly inaccurate statement as they are beyond the scope of both gods in terms of content. What would be more likely would be that sections of the books were written by multiple gods and compiled by X into two compendiums. During the wars, the mortals stole these books from X's archival library and used the tomes, including some others penned by X's Bookkeepers. From there, X is unable to retrieve these books back into his library directly, but can seal them as part of his power. That being said, why X has not recollected his books is a question to be addressed given the dangerous contents within them...
Also... what part of god of secrets did Darko mot understand? Truth, mystery and secrets. That which he rules over, he can lie and tell the truth at the same time....
Edit. The books translates itself to the reader. Knowledge without understanding is useless. Thus at the time of creation X made it the books are comprehensible by those who would read them. Also remember, these books preceded the dark and light definitions of gods. Which is why your claim to be written in a specific language should be moot.
Also... what part of god of secrets did Darko mot understand? Truth, mystery and secrets. That which he rules over, he can lie and tell the truth at the same time....
Edit. The books translates itself to the reader. Knowledge without understanding is useless. Thus at the time of creation X made it the books are comprehensible by those who would read them. Also remember, these books preceded the dark and light definitions of gods. Which is why your claim to be written in a specific language should be moot.