Select a given namespace at runtime - c++

Question

Say I have these namespaces:
namespace old
{
std::array<std::string,1> characters {"old"};
}
namespace young
{
std::array<std::string,1> characters {"young"};
}
Then I want the user to tell me at the beginning which version is he using. Then call the appropriate namespace throughout the program.
I have tried using namespace depending on input, but it doesn't work because I need to call the correct namespace in functions on other source files. I was thinking maybe can I send the namespace as a function parameter? Or do something clever with templates?
EDIT:
When I refer to "user" I mean somebody that is using my executable, a person playing my game.
What I want to do is to ask him the version he is going to use e.g. US version (things have some names), or UK version (things have other names).
All that changes is the names I use. But I want him to be able to switch between versions every time.
I hope it is clear, please let me know if you need further clarification.

Answer 1

There is no way to pass a namespace as function parameter or template parameter. User may use it as:
using namespace old;
characters[0] = 'O';
or code as:
old::characters[0] = 'O';
UPDATE: After updating original question
Namespaces are relevant during compile-time and do not reflect any behavior in runtime. What you need is more along the lines of:
enum Language
{
ENGLISH_UK, ENGLISH_US
};
std::array<std::string, 2> label = {
"colour", // for British-english
"color" // for US-English
};
And then in the code:
static Language lang = ENGLISH_UK;
std::cout << label[lang] << std::endl;
So, if there is a change in user interface, you do not need to recompile the whole app.

Answer 2

Short answer is no, because what functions are called and what variables are accessed at a particular location in your code when you e.g. write characters is detrmined at compile-time.
The slightly longer answer is that you can create wrapper functions and references in a separate namespace and let them forward to one or the other depending on the user (as long as the types are the same).
E.g.
namespace current {
int namespace_to_use = 1; // can be set by some initialization function in your code
std::array<std::string,1>& get_characters(){
return namespace_to_use == 0 ? old::characters : young::characters;
}
}
I wouldn't call that good application design and there are many more advanced/better versions of this (e.g. based on dynamic polymorphism and the factory pattern or pointers/references). What fits best depends on your needs and your level of expereience.