improve locale detection as much as possible

src/frontend/locale/langs.cpp

@@ -77,6 +77,7 @@ void langs::loadLocalesInfo(const path& resdir, string& fallback) {
 
     auto langs = root->obj("langs");
     if (langs) {
+        std::cout << "locales ";
         for (auto& entry : langs->map) {
             auto langInfo = entry.second;
 
@@ -87,9 +88,31 @@ void langs::loadLocalesInfo(const path& resdir, string& fallback) {
                 continue;
             }
 
-            std::cout << "locale " << entry.first << " (" << name << ") added" << std::endl;
+            std::cout << "[" << entry.first << " (" << name << ")] ";
             langs::locales_info[entry.first] = LocaleInfo {entry.first, name};
         } 
+        std::cout << "added" << std::endl;
+    }
+}
+
+std::string langs::locale_by_envlocale(const std::string& envlocale, const path& resdir){
+    string fallback = FALLBACK_DEFAULT;
+    if (locales_info.size() == 0) {
+        loadLocalesInfo(resdir, fallback);
+    }
+    if (locales_info.find(envlocale) != locales_info.end()) {
+        std::cout << "locale " << envlocale << " is automatically selected" << std::endl;
+        return envlocale;
+    }
+    else {
+        for (const auto& loc : locales_info) {
+            if (loc.first.find(envlocale.substr(0, 2)) != std::string::npos) {
+                std::cout << "locale " << loc.first << " is automatically selected" << std::endl;
+                return loc.first;
+            }
+        }
+        std::cout << "locale " << fallback << " is automatically selected" << std::endl;
+        return fallback;
     }
 }