Straight: Marcy is given an ancient book of magical spells that has been handed down for generations. The tome holds vast mystical powers and can easily help her defeat all her enemies. Unfortunately, the wizard who gave her the book didn't consider the fact that it was written ages ago in the ancient tongue of magic... And he succumbed to the Mentor Occupational Hazard before he could help with any translations, leaving her to muddle through on her own.
Downplayed: Marcy has some difficulty reading the spellbook, but not much.
Justified: The writers of the book assumed that The Chosen One would have adequate training to learn the language and the spells, but Emperor Evulz offed The Mentor before the training could be completed.
Although Marcy hasn't been able to learn the language of magic the book is written in, being The Chosen One means she is able to pick it up remarkably quickly all by herself. She is soon able to understand the entire book.
While Emperor Evulz has prevented Marcy from making use of the book of spells, it turns out that the book of spells wasn't necessary to begin with. Evulz leaves, content that he's crippled any attempts to stop him when Marcy eventually stops him in some other way.
Marcy can't understand the language the book is written in, but she can still cast the spells and figures out what they do on her own.
Double Subverted: Although being The Chosen One gives Marcy an innate ability to understand part of the language, this only takes her so far; much of the work remains illegible to her except for a few handy fragments.
Parodied: Unable to read a single letter in the spellbook, Marcy uses its as a blugeoning weapon instead. Amazingly, this works because of all the protective, anti-evil wards on it.
Zig Zagged: Marcy's understanding of the book fluctuates — on some days she can understand the whole thing, on others she only gets a few fragments.
Marcy's mentor isn't iced, and is thus able to guide her through understanding the book of spells and her role as The Chosen One.
Marcy understands the book on her own.
Enforced: "This spellbook has the potential to be a real Deus ex Machina, and we don't want to make things too easy for Marcy..."
Lampshaded: "Some mentor he turned out to be. He could have at least taught me the magic alphabet before getting himself killed."
Invoked: Emperor Evulz intentionally targets Marcy's mentor before he is able to teach Marcy anything of use, thus putting Marcy on an immediate back-foot.
Defied: Marcy's mentor has prepared for the possibility of his death by binding his soul to the book; if his body dies, his soul will live on in the book and thus will be able to continue guiding Marcy on her journey.
Conversed: "Why didn't the guy just call back when he was out of the tunnel instead of making assumptions?"
Deconstructed: Being unable to use the key weapon in her armory means that Marcy is critically hampered in her mission, and is soon killed.
Reconstructed: Being The Chosen One means that Marcy is resourceful and capable of lateral thinking, which helps overcome the shortfalls that her lack of understanding of the book bring. In fact, many of her enemies find this makes her more dangerous; they are so used to preparing to fight The Chosen One with full access to her book of spells that they have based all their tactics around it, and thus are completely unprepared for someone who, without being able to use the book, has had to find alternative ways of beating her enemies.
Played For Laughs: Marcy can almost read some of the spells, but not quite, and her mistranslations lead to surreal and strange effects, like turning Emperor Evulz's hair into flowers and making his dragon breathe pink bubbles instead of fire.
Played For Drama: Marcy's mistranslations cause her to miss some vital information — mainly, the book instructs her not to perform certain tasks, but all she can understand are the steps involved, not the warning...