old wives tale................  

I've never heard of this before. But I have heard if you see a white moth or a lot of lady bugs it is a sign of better things ahead for you. And I have heard if you see an owl during daylight hours a loved one will die. Also I have heard that a crow carry's the spirit of the soul. My grandmother was Native American / Cherokee & she knew a lot of these things & believed in herbal cures. I believe in herbal cures & I believe there is a lot of things out there that is also unknown to human kind.

Butterflies are my favorite creature on earth, and I am familiar with a lot of folklore associated with them. I have actually never heard the one that you mentioned, but I think that it's beautiful. I don't know if I'd say that I believe it, but I also wouldn't say that it's impossible. For those who do believe it I'm sure it's a comforting thing.
Another bit of folklore about butterflies comes from certain Native American/American Indian traditions. They say that if you have a wish or a prayer, to whisper it to a butterfly and the butterfly will carry your request to the Great Spirit.
There is also a superstition that if the first butterfly you see in the spring is white, then you will have a good year. A couple of days ago I saw a black butterfly, so I wonder what kind of year is in store for me? :-)

I have heard of that in some English movies but I don't really believe in that.

Whether it's true or not, I think it's a really beautiful idea.