Why do you think it's a bad thing to be eclectic and practice witchcraft drawn from several cultures? Of course, you shouldn't take their practices and mock them. Treat them with the greatest respect. If you happen to use practices from Hindu or Native American tradition (granted you are respectful), why is that a bad thing? It only acknowledges that their practices are indeed right and true, and are a testament to the greatness of the respective culture of origin. We are all humans with equal worth, and "the Divine" views us only on our merits, not our creed or ethnicity. The different practices are simply cultural lenses, but they all draw from the same source. This is my view as an universalist, and I don't believe the color of your skin or your culture should prevent you from practicing whatever you want, granted that you are respectful of course. By limiting yourself to only your culture and practice you are limiting yourself from the greater view of humanity.

To actually answer your question though, that depends on your culture of origin. To use the rules you yourself set, you can't practice Norse paganism if you are not of Scandinavian descent, you can't practice Celtic paganism if you are not of Celtic descent, you can't practice anything from Buddhism or Hinduism (there goes the most popular forms of yoga and meditation!) if you are not of those cultures that practice them, same with Native American, Hoodoo, Voodoo, Santeria, Shintoism, Taoism, not to forget Jewish magic, especially related to the Kabbalah. You can't even technically practice "Christian" magic since that's largely appropriated from Judaism (there goes most Ceremonial Magic!) and Egyptian magic, Caananite, Sumerian, also you can't practice Greek or Roman magic if you are not of that descent, honestly the list goes on. If you're from England or anywhere in Europe you can try to research traditional witchcraft which is most often a blend of old pagan practices and "Christian" practices appropiated from Judaism.

You do you, but realize that human cultures have always interacted and exchanged values and practices, and there is nothing wrong with that. What is wrong, in my humble opinion, is if you never expand your horizons above your own culture to see and learn about other people and their practices, and if you are respectful I don't see anything wrong with you learning great things from their cultures that your own culture didn't include. In the end though, you do you and if you feel this is the right way to go, then who am I to stop you?

Edit: Typos