To be fair, I enjoyed reading The Da Vinci Code and Dan Brown's other books even though I knew they were wrong.
Although a closer inspection reveals that not only does Dan Brown fail at history, religion, math, common sense, and simple fact-checking, but he also fails at languages and linguistics.
In Digital Fortress, there is "a short description involving decrypting a code that is wrong on several levels. Firstly, the code was thought by the characters to be "Mandarin symbols", when Mandarin is a spoken oral dialect. The character then realizes that the symbols are "Kanji language", but Kanji is a component in the Japanese writing system, not a language of its own. It is further ridiculous to think that anyone could confuse Chinese with Japanese, as Japanese writing makes use of another set of characters, kana, which are not present in Chinese. Finally, the code is decrypted out of sequence, for security purposes. Translating Chinese or Japanese out of sequence would be just as impossible as reading English text scrambled by a randomizer."
Dan Brown also fails at Italian and French. I know there was a part in the book where characters are supposedly speaking in French, but the sentences are completely incorrect translations of what they were trying to say. I'll have to find it.