javafx-localization-runtime-language

name	javafx-localization-runtime-language
description	Localize JavaFX applications with resource bundles, locale-aware formatting, and runtime language switching.
triggers	["javafx localization","runtime language switch javafx","resourcebundle javafx","javafx i18n"]
compatibility	{"java":"17+","javafx":"21+"}
category	ui-core
tags	["localization","i18n","resourcebundle","locale","translation"]
metadata	{"scope":"repository","maturity":"starter"}
allowed-tools	["view","rg","apply_patch"]

JavaFX Localization and Runtime Language

Use this skill when the UI must support multiple locales, runtime language switching, or locale-sensitive formatting. Libraries such as Language Manager show that dynamic switching is a meaningful JavaFX use case beyond startup-only resource bundles.

Example

import java.util.Locale;
import java.util.ResourceBundle;
import javafx.beans.binding.Bindings;
import javafx.beans.property.ObjectProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.layout.VBox;

public class LocalizedView extends VBox {

    private final ObjectProperty<Locale> locale = new SimpleObjectProperty<>(Locale.ENGLISH);

    public LocalizedView() {
        var label = new Label();
        var switchButton = new Button();

        label.textProperty().bind(Bindings.createStringBinding(
                () -> bundle().getString("greeting"),
                locale
        ));

        switchButton.textProperty().bind(Bindings.createStringBinding(
                () -> bundle().getString("switchLanguage"),
                locale
        ));

        switchButton.setOnAction(event -> locale.set(
                locale.get().equals(Locale.ENGLISH) ? Locale.GERMAN : Locale.ENGLISH
        ));

        getChildren().addAll(label, switchButton);
    }

    private ResourceBundle bundle() {
        return ResourceBundle.getBundle("i18n.messages", locale.get());
    }
}

Setup notes

• Keep locale state centralized so text, formatting, and selection widgets switch together.
• Use resource bundles for UI strings and separate them from domain-content translation logic.
• Plan for longer translated text and culture-specific formatting early in the layout.

Gotchas

• Runtime language switching needs binding-aware text resolution, not one-time label assignment.
• Translation keys should be stable identifiers, not English strings reused as keys.
• Locale-aware formatting affects numbers, dates, and currency, not just labels.