diff --git a/src/app.cpp b/src/app.cpp
index 58cb7ac..aaea9c0 100644
--- a/src/app.cpp
+++ b/src/app.cpp
@@ -96,13 +96,13 @@ Wt::WLocale App::determineLocaleFromBrowser() const {
         std::string lower = tag;
         std::transform(lower.begin(), lower.end(), lower.begin(), ::tolower);
 
-        // Sprache und Region trennen
+        // Sprache und Region trennen (Unterstützung für '-' und '_')
         std::string lang = lower;
         std::string region;
-        auto dashPos = lower.find('-');
-        if (dashPos != std::string::npos) {
-            lang = lower.substr(0, dashPos);
-            region = lower.substr(dashPos + 1);
+        auto sepPos = lower.find_first_of("-_");
+        if (sepPos != std::string::npos) {
+            lang = lower.substr(0, sepPos);
+            region = lower.substr(sepPos + 1);
         }
 
         if (lang == "en") {
@@ -140,17 +140,11 @@ Wt::WLocale App::determineLocaleFromBrowser() const {
         }
     }
 
-    // 2. Sonst Accept-Language Header des Browsers auswerten
-    std::string accept = env_.headerValue("Accept-Language");
-    if (!accept.empty()) {
-        std::stringstream ss(accept);
-        std::string part;
-        while (std::getline(ss, part, ',')) {
-            auto localeName = mapLanguageTag(part);
-            if (!localeName.empty()) {
-                return makeLocale(localeName);
-            }
-        }
+    // 2. Sonst Locale verwenden, die Wt bereits aus dem Browser/Request ermittelt hat
+    auto envLocaleName = env_.locale().name(); // z.B. "de_DE", "en_GB"
+    auto mapped = mapLanguageTag(envLocaleName);
+    if (!mapped.empty()) {
+        return makeLocale(mapped);
     }
 
     // Fallback: britisches Englisch