[streambuf.virt.locales]
31 Input/output library [input.output]
31.6 Stream buffers [stream.buffers]
31.6.3 Class template basic_streambuf [streambuf]
31.6.3.5 Virtual functions [streambuf.virtuals]
31.6.3.5.1 Locales [streambuf.virt.locales]
void imbue(const locale&);