The code is based on the ErrorDescription library.

Library contains ErrorDescription() function with two input parameters error_code and optional parameter txt_prefix.

string ErrorDescription(int error_code,string txt_prefix="")

GetLastError() return codes can be found here https://www.mql5.com/en/docs/constants/errorswarnings/errorcodes.

OrderSend() function's retcode field values can be found in https://www.mql5.com/en/docs/constants/errorswarnings/enum_trade_return_codes.

Both tables are included in ErrorDescription() function.

LibraryTest.mq5 script can be used to check description of a known error code. Just execute script with an input error_value set to error code and it will print description. If error_value is set to -1 script will print all available error codes.