Document server.servlet.encoding.* configuration properties

Closes gh-32472

Author: wilkinsona

spring-boot-project/spring-boot-docs/src/docs/asciidoc/web/servlet.adoc

@@ -611,6 +611,27 @@ For example, adding the following bean will automatically apply a `SameSite` of
 include::code:MySameSiteConfiguration[]
 
 
+[[web.servlet.embedded-container.customizing.encoding]]
+===== Character Encoding
+The character encoding behavior of the embedded servlet container for request and response handling can be configured using the `server.servlet.encoding.*` configuration properties.
+
+When a request's `Accept-Language` header indicates a locale for the request it will be automatically mapped to a charset by the servlet container.
+Each containers providers default locale to charset mappings and you should verify that they meet your application's needs.
+When they do not, use the configprop:server.servlet.encoding.mapping[] configuration property to customize the mappings, as shown in the following example:
+
+[source,yaml,indent=0,subs="verbatim",configprops,configblocks]
+----
+	server:
+	  servlet:
+	    encoding:
+	      mapping:
+	        ko: "UTF-8"
+----
+
+In the preceding example, the `ko` (Korean) locale has been mapped to `UTF-8`.
+This is equivalent to a `<locale-encoding-mapping-list>` entry in a `web.xml` file of a traditional war deployment.
+
+
 
 [[web.servlet.embedded-container.customizing.programmatic]]
 ===== Programmatic Customization