web/play-java-forms/src/main/java/play/data/Form.java
public Form<T> withLang(Lang lang) {
    return new Form<T>(
        this.rootName,
        this.backedType,
        this.rawData,
        this.files,
        this.errors,
        this.value,
        this.groups,
        this.messagesApi,
        this.formatters,
        this.validatorFactory,
        this.config,
        lang,
        this.directFieldAccess);
  }
public Form<T> withLang(Lang lang) {
    return new Form<T>(
        this.rootName,
        this.backedType,
        this.rawData,
        this.files,
        this.errors,
        this.value,
        this.groups,
        this.messagesApi,
        this.formatters,
        this.validatorFactory,
        this.config,
        lang,
        this.directFieldAccess);
  }
A copy of this form with the given lang set which is used for formatting when retrieving a
field (via {@link #field(String)} or {@link #apply(String)}) and for translations in {@link
#errorsAsJson()}.