fixes #672 add multiple language doc

Author: stevehu

README.md

@@ -125,6 +125,9 @@ For the latest version, please check the [release](https://github.com/networknt/
 
 ## [Custom Message](doc/cust-msg.md)
 
+## [Multiple Language](doc/multiple-language.md)
+
+
 ## Known issues
 
 I have just updated the test suites from the [official website](https://github.com/json-schema-org/JSON-Schema-Test-Suite) as the old ones were copied from another Java validator. Now there are several issues that need to be addressed. All of them are edge cases, in my opinion, but need to be investigated. As my old test suites were inherited from another Java JSON Schema Validator, I guess other Java Validator would have the same issues as these issues are in the Java language itself.

doc/multiple-language.md

@@ -0,0 +1,12 @@
+The error messages have been translated to several languages by contributors. Here is the code to use German.
+
+```
+Locale.setDefault(Locale.GERMAN);
+JsonSchemaFactory jsonFactoryInstance = JsonSchemaFactory.getInstance(SpecVersion.VersionFlag.V202012);
+JsonSchemaFactory schemaFactory = JsonSchemaFactory.builder(jsonFactoryInstance).build();
+```
+
+To add other languages, we need to add properties file under this folder. 
+
+https://github.com/networknt/json-schema-validator/tree/master/src/main/resources
+