Umbraco Localization

What is it?

Localization enables UI translation through localization files managed by the Extension Registry, with English (iso code: ‘en’) as the fallback language. The Localization Controller (automatically available in Umbraco Elements via this.localize) provides access to translated strings using keys. Custom translations can be added via the Extension Registry and referenced in manifests using the # prefix.

Documentation

Always fetch the latest docs before implementing:

• Main docs: https://docs.umbraco.com/umbraco-cms/customizing/foundation/localization
• Foundation: https://docs.umbraco.com/umbraco-cms/customizing/foundation
• Extension Registry: https://docs.umbraco.com/umbraco-cms/customizing/extending-overview/extension-registry

Workflow

1. Fetch docs – Use WebFetch on the URLs above
2. Ask questions – Using built-in keys or custom? Need pluralization? Dynamic values?
3. Generate code – Implement localization based on latest docs
4. Explain – Show what was created and how to test

Minimal Examples

Using Localize Controller (Umbraco Element)

import { html, customElement } from '@umbraco-cms/backoffice/external/lit';
import { UmbLitElement } from '@umbraco-cms/backoffice/lit-element';

@customElement('my-element')
export class MyElement extends UmbLitElement {
  render() {
    return html`
      <uui-button .label=${this.localize.term('general_close')}>
        ${this.localize.term('general_close')}
      </uui-button>
      <p>${this.localize.term('general_welcome')}</p>
    `;
  }
}

Using Localize Controller with fallback (Umbraco 17.1+ only!)

import { html, customElement } from '@umbraco-cms/backoffice/external/lit';
import { UmbLitElement } from '@umbraco-cms/backoffice/lit-element';

@customElement('my-element')
export class MyElement extends UmbLitElement {
  render() {
    return html`
      <p>Renders "Welcome": ${this.localize.term('general_welcome')}</p>
      <p>Renders "This is a fallback": ${this.localize.termOrDefault('test_unavailable', 'This is a fallback')}</p>
    `;
  }
}

Using Localize Element

render() {
  return html`
    <button>
      <umb-localize key="dialog_myKey">Default Text</umb-localize>
    </button>
  `;
}

Manual Localize Controller

import { UmbLocalizationController } from '@umbraco-cms/backoffice/localization-api';
import { UmbControllerBase } from '@umbraco-cms/backoffice/class-api';

export class MyController extends UmbControllerBase {
  #localize = new UmbLocalizationController(this);

  render() {
    return html`
      <uui-button .label=${this.#localize.term('general_close')}>
      </uui-button>
    `;
  }
}

Custom Localization File

// en.js
export default {
  myExtension: {
    welcomeMessage: 'Welcome to my extension!',
    itemCount: 'You have {0} items',
    goodbye: 'Goodbye, {0}!',
  },
};

Registering Custom Localizations

// manifest.ts
export const manifests = [
  {
    type: 'localization',
    alias: 'My.Localization.En',
    name: 'English Localization',
    meta: {
      culture: 'en',
    },
    js: () => import('./localization/en.js'),
  },
];

Using Custom Keys

render() {
  return html`
    <h1>${this.localize.term('myExtension_welcomeMessage')}</h1>
    <p>${this.localize.term('myExtension_itemCount', 5)}</p>
  `;
}

Localization with Arguments

// Localization file with function
export default {
  section: {
    numberOfItems: (count) => {
      if (count === 0) return 'Showing nothing';
      if (count === 1) return 'Showing only one item';
      return `Showing ${count} items`;
    },
  },
};

// Usage
render() {
  return html`
    <umb-localize
      key="section_numberOfItems"
      .args=${[this._itemCount]}
    ></umb-localize>
  `;
}

Localize in Manifest

{
  "type": "dashboard",
  "alias": "My.Dashboard",
  "name": "My Dashboard",
  "meta": {
    "label": "#welcomeDashboard_label",
    "pathname": "welcome"
  }
}

Common Built-in Keys

// General
this.localize.term('general_close')
this.localize.term('general_cancel')
this.localize.term('general_save')
this.localize.term('general_delete')
this.localize.term('general_welcome')

// Actions
this.localize.term('actions_create')
this.localize.term('actions_edit')
this.localize.term('actions_remove')

// Dialogs
this.localize.term('dialog_confirm')
this.localize.term('dialog_cancel')

Debug Mode

<!-- Shows the key alias instead of value for troubleshooting -->
<umb-localize key="myExtension_welcomeMessage" debug="true"></umb-localize>

Multiple Languages

// en.js
export default {
  greeting: 'Hello',
};

// da.js (Danish)
export default {
  greeting: 'Hej',
};

// Register both
export const manifests = [
  {
    type: 'localization',
    alias: 'My.Localization.En',
    meta: { culture: 'en' },
    js: () => import('./localization/en.js'),
  },
  {
    type: 'localization',
    alias: 'My.Localization.Da',
    meta: { culture: 'da' },
    js: () => import('./localization/da.js'),
  },
];

Key Concepts

Localize Controller: Auto-available in Umbraco Elements via this.localize

Translation Keys: Use underscore notation (e.g., general_close, myExtension_welcomeMessage)

Fallback: English (en) is the default fallback when translations are missing – all extensions should, as a minimum, include an ‘en’ localization manifest

Default text: If unsure whether the localization key exists, or for easier readability, add a default text to <umb-localize key="section_key">Default text</umb-localize> or as second argument to termOrDefault()

Arguments: Pass dynamic values using .args attribute or second parameter to term()

Manifest Localization: Prefix values with # to reference translation keys

Debug Mode: Use debug="true" to show key aliases for troubleshooting

File Structure:

• One file per language (en.js, da.js, etc.)
• Export default object with nested keys
• Register via Extension Registry

That’s it! Always fetch fresh docs, keep examples minimal, generate complete working code.