Thread:Pythonraptor/@comment-4097945-20130621134031/@comment-3087943-20130622172221

Well, there's no "grammatically correct" reason to omit a kanji's meaning in a translation, simply because there are no set rules when using kanji for techniques names, other than phonetic rules, and even they can sometimes be omitted. Many Indian and Buddhist words are written in Japanese with kanji that make sense only in their pronunciation, not their meaning. For example, I plan to make an article about a snake user, and he/she will summon giant snakes known as the. Now, the kanji used literally mean "Polished Silk", which of course make no sense. However, as they do give an accurate phonetic representation of the Buddhist "Mahoraga", they are used.

So, to answer your question, there are no preset rules for spelling certain words in kanji, they simply have to be memorized. 曼陀羅 is used for "mandala" simply because it's pronounced in much the same way.