diff --git a/autotests/kxmlgui_unittest.cpp b/autotests/kxmlgui_unittest.cpp
--- a/autotests/kxmlgui_unittest.cpp
+++ b/autotests/kxmlgui_unittest.cpp
@@ -1086,6 +1086,7 @@
     KDEPrivate::initializeLanguages();
 
     QCOMPARE(QLocale::system().language(), QLocale::Russian);
+    QCOMPARE(QLocale::system().monthName(1), QString::fromUtf8("января"));
 
     KDEPrivate::setApplicationSpecificLanguage("wa");
     KDEPrivate::initializeLanguages();
diff --git a/src/kswitchlanguagedialog_p.cpp b/src/kswitchlanguagedialog_p.cpp
--- a/src/kswitchlanguagedialog_p.cpp
+++ b/src/kswitchlanguagedialog_p.cpp
@@ -80,18 +80,24 @@
     }
 }
 
+void addSetEnvVar(const char *envVarName, const QByteArray &value)
+{
+    const QByteArray envVarValue = qgetenv(envVarName);
+    if (envVarValue.isEmpty()) {
+        qputenv(envVarName, value);
+    } else {
+        qputenv(envVarName, value + ':' + envVarValue);
+    }
+}
+
 void initializeLanguages()
 {
     const QByteArray languageCode = getApplicationSpecificLanguage();
 
     if (!languageCode.isEmpty()) {
-        QByteArray languages = qgetenv("LANGUAGE");
-        if (languages.isEmpty()) {
-            qputenv("LANGUAGE", languageCode);
-        } else {
-            qputenv("LANGUAGE", languageCode + ':' + languages);
-        }
-        // Ideally setting the LANGUAGE would change the default QLocale too
+        addSetEnvVar("LANGUAGE", languageCode);
+        addSetEnvVar("LC_ALL", languageCode);
+        // Ideally setting LANGUAGE/LC_ALL would change the default QLocale too
         // but unfortunately this is too late since the QCoreApplication constructor
         // already created a QLocale at this stage so we need to set the reset it
         // by triggering the creation and destruction of a QSystemLocale