MdePkg: UefiLib: Add a function to check if a language is supported

Add a function that checks if a target language is in the supported
languages list. Add some calls to this function where appropriate in
UefiLib.c

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Tom Zhao <tzhao@solarflare.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

MdePkg/Include/Library/UefiLib.h

@@ -461,6 +461,23 @@ EfiTestChildHandle (
   IN CONST EFI_GUID         *ProtocolGuid
   );
 
+/**
+ * This function checks the supported languages list for a target language,
+ * This only supports RFC 4646 Languages.
+ *
+ * @param      SupportedLanguages  The supported languages
+ * @param      TargetLanguage      The target language
+ *
+ * @return     Returns EFI_SUCCESS if the language is supported,
+ *             EFI_UNSUPPORTED otherwise
+ */
+EFI_STATUS
+EFIAPI
+IsLanguageSupported (
+  IN CONST CHAR8 *SupportedLanguages,
+  IN CONST CHAR8 *TargetLanguage
+  );
+
 /**
   This function looks up a Unicode string in UnicodeStringTable.