Fix passing gb2312 encoded strings to tts on Windows (#1819)

sherpa-onnx/csrc/text-utils.h

@@ -127,6 +127,18 @@ void ToLowerCase(std::string *in_out);
 std::string RemoveInvalidUtf8Sequences(const std::string &text,
                                        bool show_debug_msg = false);
 
+// Return true if text contains valid utf8 sequence.
+// Return false otherwise
+bool IsUtf8(const std::string &text);
+
+// Return true if text contains valid gb2312 encoded sequence
+// Return false otherwise
+bool IsGB2312(const std::string &text);
+
+#if defined(_WIN32)
+std::string Gb2312ToUtf8(const std::string &text);
+#endif
+
 }  // namespace sherpa_onnx
 
 #endif  // SHERPA_ONNX_CSRC_TEXT_UTILS_H_