Is it impolite to ask the girlfriend of the girl you like for information? Will her best friend tell her that I like her?

No, don't think too much. You just need to ask politely and respectfully. In fact, girls' girlfriends will feel very happy when they know that their good friends are liked and will help you well. Of course, people helped you. As the most basic courtesy, you can also help girls' girlfriends when you have the chance, because they have helped you. Good luck.

. . . . . . . . . . . . . . From a man who is also a man. . . . . . . . . . . . . . . .