diff --git a/dll/win32/kernel32/winnls/string/lang.c b/dll/win32/kernel32/winnls/string/lang.c
index 4841e7a9d57..c976310596a 100644
--- a/dll/win32/kernel32/winnls/string/lang.c
+++ b/dll/win32/kernel32/winnls/string/lang.c
@@ -2008,6 +2008,39 @@ INT WINAPI LCMapStringEx(LPCWSTR name, DWORD flags, LPCWSTR src, INT srclen, LPW
         }
     }
 
+#ifdef __REACTOS__
+    if (flags & LCMAP_KATAKANA)
+    {
+        INT convlen = dst_ptr - dst;
+        for (dst_ptr = dst; convlen; --convlen, ++dst_ptr)
+        {
+            /*
+             * U+3041 ... U+3093: Hiragana
+             * U+3095: Hiragana Letter Small KA
+             * U+309D: Hiragana Iteration Mark
+             */
+            WCHAR wch = *dst_ptr;
+            if ((0x3041 <= wch && wch <= 0x3093) || wch == 0x3095 || wch == 0x309D)
+                *dst_ptr = wch + 0x60; /* Hiragana to Katanaka */
+        }
+    }
+    else if (flags & LCMAP_HIRAGANA)
+    {
+        INT convlen = dst_ptr - dst;
+        for (dst_ptr = dst; convlen; --convlen, ++dst_ptr)
+        {
+            /*
+             * U+30A1 ... U+30F3: Katakana
+             * U+30F5: Katakana Letter Small KA
+             * U+30FD: Katakana Iteration Mark
+             */
+            WCHAR wch = *dst_ptr;
+            if ((0x30A1 <= wch && wch <= 0x30F3) || wch == 0x30F5 || wch == 0x30FD)
+                *dst_ptr = wch - 0x60; /* Katanaka to Hiragana */
+        }
+    }
+#endif
+
     if (srclen)
     {
         SetLastError(ERROR_INSUFFICIENT_BUFFER);