1. Setting up UTF-8 Encoding - Ensure your application.yaml file is saved in UTF-8 encoding. If non-UTF-8 encoding is used, Japanese characters otherwise not display correctly.

   messages:
     greeting: こんにちは
     farewell: さようなら
   

2. Call this properties in Java File in Spring boot through of @Value Annotation.
   @Value("${messages.greeting}")
   private String greetingMessage;

3. Using @ConfigurationProperties

@Configuration
@ConfigurationProperties(prefix = "messages")
public class MessageConfig {
    private String greeting;
    private String farewell;

    // Getters and Setters
}

If you are use Multi-language So you can handle the through of message.properties and as well as store the multi-language in Database also.