faced this same issue... added
using namespace icu
exactly the way mapkoc said.. but now i'm facing this error (screenshot):
/usr/include/c++/7.3.1/cstdlib:75:15: fatal error: stdlib.h: No such file or directory
#include_next <stdlib.h>
seriously! it's frustrating to see no maps of 0ad made the curvature of the earth in mind! Do 0ad authors are flat earthers? being a fan of 0ad I would love to see maps with the real(spherical) shape of the earth in mind. thanks