The problem is a bug of language.

Minecraft can't translate accents of spanish language in AbyssalCraft Mod (Necronomicon), for example: Í, á ,ó, etc..

Solution?

Seems like one of the translator(s) (can't remember for certain if there was one or two, heck, can't even find any traces of anyone contributing to the .lang file besides myself) changed the file encoding of the .lang file, which in turn lead to it not being loaded correctly (hence all accented characters being replaced with question marks).

Also, in the future, please use the bug report template when reporting a bug (in this instance it wasn't anything version specific, but in other instances having the Minecraft, Forge, and AbyssalCraft versions used available can be pretty crucial in solving the problem).