core/play/src/main/java/play/i18n/MessagesApi.java
public Result setLang(Result result, Lang lang) {
    return messages.setLang(result.asScala(), lang).asJava();
  }
public Result setLang(Result result, Lang lang) {
    return messages.setLang(result.asScala(), lang).asJava();
  }
Given a Result and a Lang, return a new Result with the lang cookie set to the given Lang.

@param result the result where the lang will be set.
@param lang the lang to set on the result
@return a new result with the lang.