mlang: Use a case independent compare for the RFC1766 name.

dlls/mlang/mlang.c

@@ -1197,7 +1197,7 @@ static HRESULT lcid_from_rfc1766(IEnumRfc1766 *iface, LCID *lcid, LPCWSTR rfc176
 
     while (IEnumRfc1766_Next(iface, 1, &info, &num) == S_OK)
     {
-        if (!strcmpW(info.wszRfc1766, rfc1766))
+        if (!strcmpiW(info.wszRfc1766, rfc1766))
         {
             *lcid = info.lcid;
             return S_OK;

dlls/mlang/tests/mlang.c

@@ -62,6 +62,9 @@ static const lcid_table_entry  lcid_table[] = {
 
     {"en",    9,        S_OK},       /* only en is special (using PRIMARYLANGID) */
     {"en-gb", 0x809,    S_OK},
+    {"en-GB", 0x809,    S_OK},
+    {"EN-GB", 0x809,    S_OK},
+    {"en-US", 0x409,    S_OK},
     {"en-us", 0x409,    S_OK}
 
 };