imperialism, state policy, practice, or advocacy of extending power and dominion, especially by direct territorial acquisition or by gaining political and economic control of other areas.

https://www.britannica.com/topic/imperialism

You know you can just look up these thing right?

Not taxing your citizens, is not imperialism. Luxembourg is not an imperialist country.

The process that you're describing is called free trade. As soon as the global south doesn't want to partake in this trade, they can stop. And Luxembourg wouldn't have anything to say on that matter.