On Wed, 25 Jun 2008, David Goodman wrote:
There are thousands of cases where a mistranslation or mistransliteration has caused the standard English name for a character or book or place or name to be different than in the original. That's why we need a rule, and have one, to avoid arguing over he merits of each individual instance. Once a mistake has been adopted in the english language, there it is.
Rules are always subject to IAR and common sense. You should never respond to "that doesn't make sense" with "the rules are there so we don't have to decide whether it makes sense".
The difference between Tetsusaiga and other examples of mistranslations is that the correct name is still fairly widely known and used. The wrong name, since it's published by a corporation, has spread enough to become common, but it's not so common that the correct name is unknown except to scholars. Common sense says that it's not our job to spread misinformation. The fact that a name is wrong should tilt the scale towards not using it, even if other factors sometimes outweigh this. For most mistranslations, the wrong name is *so* exclusively used that the other factors do outweigh this, so it makes sense to use the wrong name. Here, this is not so.