I18n Internationalization

Display validation errors in other languages.

If you are already using the aurelia/i18n plugin, you would also naturally want localization support for validation. The package provides out-of-the-box localization support.

The plugin has a dependency on @aurelia/i18n package. It assumes that the @aurelia/i18n package is correctly registered/configured and uses the I18N services to provide the translations.

To add localization support, you must first register the plugin.

import Aurelia from 'aurelia';
import { ValidationI18nConfiguration } from '@aurelia/validation-i18n'; // <-- get the configuration
import { I18nConfiguration } from '@aurelia/i18n';
import { MyApp } from './my-app';
import * as en from "./locales/en.json";
import * as de from "./locales/de.json";

    I18nConfiguration.customize((options) => { // <-- take care of I18N configuration as you see fit
      options.initOptions = {
        resources: {
          en: { translation: en },
          de: { translation: de },
    ValidationI18nConfiguration // <-- register the configuration

Note that the @aurelia/validation-i18n wraps the @aurelia/validation plugin. Stated differently, it customizes the @aurelia/validation plugin with custom implementations of the following:

  • Validation controller factory ( see the ValidationControllerFactoryType customization option): This ensures that the validation controller reacts to locale change.

  • Message provider (see the MessageProviderType customization option): This ensures that localized error message templates and property names are used to create the error messages. With this place, the evaluation expr in withMessageKey(expr) is used as an I18N key, and the value is looked up in the I18N resources. This also happens for the display names of the properties, where the property name is used as the I18N key.

Check the demo to see this in action.

All the configuration options of the @aurelia/validation plugin are also available from @aurelia/validation-i18n. This means it even allows you to provide your implementation of a message provider or validation controller factory! Apart from that, it has two additional configuration options that dictate how the value of the I18N keys is looked up.

  • DefaultNamespace

    By default, the value of the keys is searched in translation namespace. Using this configuration option that can be changed. This is useful if you want to separate the validation resources from your regular 18N resources. See the example below.

  • DefaultKeyPrefix

    Instead of using a separate namespace, a key prefix can be used for the keys related to validation resources. This is shown in the example below.

Naturally, the DefaultNamespace and the DefaultKeyPrefix can be used together.

It should not come as any surprise that localization also works for model-based rules when appropriate messageKey is specified in the rule definition.

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