diff --git a/reactos/ntoskrnl/include/internal/mm.h b/reactos/ntoskrnl/include/internal/mm.h
index c2b849a10d1..53ef8be0144 100644
--- a/reactos/ntoskrnl/include/internal/mm.h
+++ b/reactos/ntoskrnl/include/internal/mm.h
@@ -1798,3 +1798,8 @@ NTAPI
 MmGetSessionById(
     _In_ ULONG SessionId);
 
+_IRQL_requires_max_(APC_LEVEL)
+VOID
+NTAPI
+MmSetSessionLocaleId(
+    _In_ LCID LocaleId);
diff --git a/reactos/ntoskrnl/mm/ARM3/session.c b/reactos/ntoskrnl/mm/ARM3/session.c
index 4ce6ed58f0b..b748101899d 100644
--- a/reactos/ntoskrnl/mm/ARM3/session.c
+++ b/reactos/ntoskrnl/mm/ARM3/session.c
@@ -80,9 +80,9 @@ MmGetSessionLocaleId(VOID)
     Process = PsGetCurrentProcess();
 
     //
-    // Check if it's the Session Leader
+    // Check if it's NOT the Session Leader
     //
-    if (Process->Vm.Flags.SessionLeader)
+    if (!Process->Vm.Flags.SessionLeader)
     {
         //
         // Make sure it has a valid Session
@@ -102,6 +102,31 @@ MmGetSessionLocaleId(VOID)
     return PsDefaultThreadLocaleId;
 }
 
+_IRQL_requires_max_(APC_LEVEL)
+VOID
+NTAPI
+MmSetSessionLocaleId(
+    _In_ LCID LocaleId)
+{
+    PEPROCESS CurrentProcess;
+    PAGED_CODE();
+
+    /* Get the current process and check if it is in a session */
+    CurrentProcess = PsGetCurrentProcess();
+    if ((CurrentProcess->Vm.Flags.SessionLeader == 0) &&
+        (CurrentProcess->Session != NULL))
+    {
+        /* Set the session locale Id */
+        ((PMM_SESSION_SPACE)CurrentProcess->Session)->LocaleId = LocaleId;
+    }
+    else
+    {
+        /* Set the default locale */
+        PsDefaultThreadLocaleId = LocaleId;
+    }
+}
+
+
 VOID
 NTAPI
 MiInitializeSessionIds(VOID)