I wouldn’t say “plans” as in I’ve actually planned to add localization, but I want the package to be completely customizable so changing that label should also be made possible. One way would be to add a overall_label keyword to which you could pass "Global". But maybe it would make more sense to localize the whole package at once, by looking up the labels dynamically and the user can change how they are all looked up. For example you would also not want Mean in a Spanish table, but at some point it’s silly to keep adding x_label keywords. So one could use a new LocalizedString type internally instead and the user would pass a dictionary with all the translations. This could also maybe be done with ScopedValues.
You could open an issue for further discussion 
Currently your only option is taking the Table object, inspecting the cell array and replacing the Cell with the Overall label. That accesses internals though.