Moreover, some english strings seem to be hard-coded in program_options (exception messages, etc.) There should be another way of handling cmdline errors - we can't presume that the user understands english text. And there does not seem to be a way of translating the po exceptions to localized strings without accessing/changing some po internals.
I suspect all boost libraries share this problem, and nobody came with a nice solution for solving this.
I can surely provide a hook, specific for program_options, that is called to translate messages.
Sure, but program_options is in fact implementation of some UI so the need for user interaction is higher than with some other libraries. I think that providing some additional data members in the exception classes would be sufficient. That way, you don't need to provide any hooks at all. The current pattern for using exceptions is something like throw my_exception("some text "+param+": some other text "+param2); (sometimes the string construction is in my_exception's constructor). I'd rather see throw my_exception(param, param2); and somewhere in my_exception: class my_exception { .... public: string param; string param2; string what() const { return "some text "+param+": some other text "+param2; } } Cheers, Filip