std::stringstream gets broken after setting UTF8 locale

I'm having trouble with outputting numbers once I set a global locale in my C++ app.Here's a working code sample:

#include <locale>#include <clocale>#include <sstream>#include <iostream>void initLocale() {    constexpr char locale_name[] = "en_US.UTF-8";    std::setlocale( LC_ALL, locale_name );    std::locale::global(std::locale(locale_name));}int main() {    int64_t i = -123434534536;    std::stringstream s1;    s1 << i << "\n";    std::cout << "Before locale: " << s1.str();    initLocale();    std::stringstream s2;    s2 << i << "\n";    std::cout << "After locale: " << s2.str();    return 0;}

I compile this code on LINUX (debian) with g++ using this command:

g++ -std=c++17 -o test test.cpp

The output I get by running the program is this:

Before locale: -123434534536After locale: -123,434,534,536

Why does std::stringstream behave like this after setting the locale and how can I fix it?

P.S.:I need to use this locale in order to correctly handle non-ANSI characters in filenames (I have some files that contain Chinese characters)