I was wondering if anyone has a good spell to erase somebody's mind on something, you know... I taught my friend something I should have not: Swearing Japanese. Swearing Japanese was one of my personal things, until I told my friend. She told it to somebody who has to tell everbody what they hear- especially gossip. That person passed it on to another person. Also, my friend is swearing Japanese at people for no reason.
No spell has the ability to do that, as for your problem you should've not told that to anybody firstplace and it's your own fault and since its turned into gossip and spreading to people its going to stay out there for a while. Hence you would just have to deal with it.
That's something that is a bit more intense then you realize. Such rituals are dark and require a lot of skill and in some cases involve kidnapping the person. There are some that involve possession and there is voodon zombification (more science then magic really) but for something like that it's not worth it. So instead I'll teach you some psychology. What you do is just ignore it like the person didn't say anything whenever your friend or someone else curses in Japanese. It works like a trend it'll be forgotten but it is kept alive by the attention drawn to it. So, don't feed it. If that doesn't work then there is more that can be done.
Even if there were such a spell, you would be going into very unethical behavior to use it on someone. That knowledge you're wanting to erase isn't yours; it belongs to the person in whose mind it is now located. To erase it would be theft, a violation of that person's inner self. Do you really think you have a right to do that?
If you told your friend this information, it is now hers.