Minor Description
MessageFormatMessage uses MessageFormat,format(pattern, args), StringFormattedMessage uses String.format(pattern, args) both are using the default Locale to format the numbers.
Sometime it is desirable/needed to use a specific locale (for instance LOG4J2-1276, or for a system running in one locale but which logs are exploited in another), therefore FormattedMessage, MessageFormatMessage and StringFormattedMessage should support passing in a Locale to ensure appropriate formatting.