I18n

Kibana relies on several UI frameworks (ReactJS and AngularJS) and requires localization in different environments (browser and NodeJS). Internationalization engine is framework agnostic and consumable in all parts of Kibana (ReactJS, AngularJS and NodeJS). In order to simplify internationalization in UI frameworks, the additional abstractions are built around the I18n engine: react-intl for React and custom components for AngularJS. React-intl is built around intl-messageformat, so both React and AngularJS frameworks use the same engine and the same message syntax.

Localization files

Localization files are JSON files.

Using comments can help to understand which section of the application the localization key is used for. Also namespaces are used in order to simplify message location search. For example, if we are going to translate the title of /management/sections/objects/_objects.html file, we should use message path like this: 'management.objects.objectsTitle'.

Each Kibana plugin has a separate folder with translation files located at

{path/to/plugin}/translations/{locale}.json

where locale is ISO 639 language code.

For example:

src/legacy/core_plugins/kibana/translations/fr.json

The engine scans x-pack/plugins/*/translations, src/core_plugins/*/translations, plugins/*/translations and src/legacy/ui/translations folders on initialization, so there is no need to register translation files.

The engine uses a config/kibana.yml file for locale resolution process. If locale is defined via i18n.locale option in config/kibana.yml then it will be used as a base locale, otherwise i18n engine will fall back to en. The en locale will also be used if translation can't be found for the base non-English locale.

One of our technical requirements is to have default messages in the templates themselves, and those messages will always be in English, so we don't have to keep en.json file in repository. We can generate that file from defaultMessages defined inline.

Note: locale defined in i18n.locale and the one used for translation files should match exactly, e.g. i18n.locale: zh and .../translations/zh-CN.json won't match and default English translations will be used, but i18n.locale: zh-CN and.../translations/zh-CN.json or i18n.locale: zh and .../translations/zh.json will work as expected.

Note: locale should look like zh-CN where zh - lowercase two-letter or three-letter ISO-639 code and CN - uppercase two-letter ISO-3166 code (optional). ISO-639 and ISO-3166 codes should be separated with - character.

I18n engine

I18n engine is the platform agnostic abstraction that helps to supply locale data to UI frameworks and provides methods for the direct translation.

Here is the public API exposed by this engine:

addMessages(messages: Map<string, string>, [locale: string]) - provides a way to register translations with the engine
getMessages() - returns messages for the current language
setLocale(locale: string) - tells the engine which language to use by given language key
getLocale() - returns the current locale
setDefaultLocale(locale: string) - tells the library which language to fallback when missing translations
getDefaultLocale() - returns the default locale
setFormats(formats: object) - supplies a set of options to the underlying formatter. For the detailed explanation, see the section below
getFormats() - returns current formats
getRegisteredLocales() - returns array of locales having translations
translate(id: string, { values: object, defaultMessage: string, description: string }) – translate message by id. description is optional context comment that will be extracted by i18n tools and added as a comment next to translation message at defaultMessages.json.
init(messages: Map<string, string>) - initializes the engine

I18n engine internals

The engine uses the ICU Message syntax and works for all CLDR languages which have pluralization rules defined. It's built around intl-messageformat package which exposes IntlMessageFormat class. Messages are provided into the constructor as a string message, or a pre-parsed AST object.

import IntlMessageFormat from 'intl-messageformat';

const msg = new IntlMessageFormat(message, locales, [formats]);

The string message is parsed, then stored internally in a compiled form that is optimized for the format() method to produce the formatted string for displaying to the user.

const output = msg.format(values);

formats parameter in IntlMessageFormat constructor allows formatting numbers and dates/times in messages using Intl.NumberFormat and Intl.DateTimeFormat, respectively.

const msg = new IntlMessageFormat('The price is: {price, number, USD}', 'en-US', {
  number: {
    USD: {
      style   : 'currency',
      currency: 'USD',
    },
  },
});

const output = msg.format({ price: 100 });

console.log(output); // => "The price is: $100.00"

In this example, we're defining a USD number format style which is passed to the underlying Intl.NumberFormat instance as its options. Here you can find default format options used as the prototype of the formats provided to the constructor.

Creating instances of IntlMessageFormat is expensive. Intl-format-cache library is simply to make it easier to create a cache of format instances of a particular type to aid in their reuse. Under the hood, this package creates a cache key based on the arguments passed to the memoized constructor.

import memoizeIntlConstructor from 'intl-format-cache';

const getMessageFormat = memoizeIntlConstructor(IntlMessageFormat);

Vanilla JS

Intl-messageformat package assumes that the Intl global object exists in the runtime. Intl is present in all modern browsers and Node.js 0.10+. In order to load i18n engine in Node.js we should simply import this module (in Node.js, the data for all 200+ languages is loaded along with the library) and pass the translation messages into init method:

import { i18n } from '@kbn/i18n';

i18n.init(messages);

One common use-case is that of internationalizing a string constant. Here's an example of how we'd do that:

import { i18n } from '@kbn/i18n';

export const HELLO_WORLD = i18n.translate('hello.wonderful.world', {
  defaultMessage: 'Greetings, planet Earth!',
});

One more example with a parameter:

import { i18n } from '@kbn/i18n';

export function getGreetingMessage(userName) {
  return i18n.translate('hello.wonderful.world', {
    defaultMessage: 'Greetings, {name}!',
    values: { name: userName },
    description: 'This is greeting message for main screen.'
  });
}

We're also able to use all methods exposed by the i18n engine (see I18n engine section above for more details).

React

React-intl library is used for internalization React part of the application. It provides React components and an API to format dates, numbers, and strings, including pluralization and handling translations.

React Intl uses the provider pattern to scope an i18n context to a tree of components. IntlProvider component is used to setup the i18n context for a tree. After that we are able to use FormattedMessage component in order to translate messages. IntlProvider should wrap react app's root component (inside each react render method).

In order to translate messages we need to use I18nProvider component that uses I18n engine under the hood:

import React from 'react';
import ReactDOM from 'react-dom';
import { I18nProvider } from '@kbn/i18n/react';

ReactDOM.render(
  <I18nProvider>
    <RootComponent>
      ...
    </RootComponent>
  </I18nProvider>,
  document.getElementById('container')
);

After that we can use FormattedMessage components inside RootComponent:

import React, { Component } from 'react';
import { FormattedMessage } from '@kbn/i18n/react';

class RootComponent extends Component {
  constructor(props) {
    super(props);

    this.state = {
      name: 'Eric',
      unreadCount: 1000,
    };
  }

  render() {
    const {
      name,
      unreadCount,
    } = this.state;

    return (
      <p>
        <FormattedMessage
          id="welcome"
          defaultMessage="Hello {name}, you have {unreadCount, number} {unreadCount, plural,
            one {message}
            other {messages}
          }"
          values={{name: <b>{name}</b>, unreadCount}}
        />
        ...
      </p>
    );
  }
}

Optionally we can pass description prop into FormattedMessage component. This prop is optional context comment that will be extracted by i18n tools and added as a comment next to translation message at defaultMessages.json

NOTE: To minimize the chance of having multiple I18nProvider components in the React tree, try to use I18nProvider only to wrap the topmost component that you render, e.g. the one that's passed to reactDirective or ReactDOM.render.

FormattedRelative

FormattedRelative expects several attributes (read more here), including

value that can be parsed as a date,
formats that should be one of 'years' | 'months' | 'days' | 'hours' | 'minutes' | 'seconds' (this options are configured in formats.ts)
etc.

If formats is not provided then it will be chosen automatically:
x seconds ago for x < 60, 1 minute ago for 60 <= x < 120, etc.

<FormattedRelative
  value={Date.now() - 90000}
  format="seconds"
/>

Initial result: 90 seconds ago

<FormattedRelative
  value={Date.now() - 90000}
/>

Initial result: 1 minute ago

Attributes translation in React

The long term plan is to rely on using FormattedMessage and i18n.translate() by statically importing i18n from the @kbn/i18n package. Avoid using injectI18n and rely on i18n.translate() instead.

React wrapper provides an ability to inject the imperative formatting API into a React component via its props using injectI18n Higher-Order Component. This should be used when your React component needs to format data to a string value where a React element is not suitable; e.g., a title or aria attribute. In order to use it you should wrap your component with injectI18n Higher-Order Component. The formatting API will be provided to the wrapped component via props.intl.

React component as a pure function:

import React from 'react';
import { injectI18n, intlShape } from '@kbn/i18n/react';

export const MyComponent = injectI18n({ intl }) => (
  <input
    type="text"
    placeholder={intl.formatMessage(
      {
        id: 'welcome',
        defaultMessage: 'Hello {name}, you have {unreadCount, number}\
{unreadCount, plural, one {message} other {messages}}',
        description: 'Message description',
      },
      { name, unreadCount }
    )}
  />
));

MyComponent.WrappedComponent.propTypes = {
  intl: intlShape.isRequired,
};

React component as a class:

import React from 'react';
import { injectI18n, intlShape } from '@kbn/i18n/react';

export const MyComponent = injectI18n(
  class MyComponent extends React.Component {
    static propTypes = {
      intl: intlShape.isRequired,
    };

    render() {
      const { intl } = this.props;

      return (
        <input
          type="text"
          placeholder={intl.formatMessage({
            id: 'kbn.management.objects.searchPlaceholder',
            defaultMessage: 'Search',
          })}
        />
      );
    }
  }
);

AngularJS

The long term plan is to rely on using i18n.translate() by statically importing i18n from the @kbn/i18n package. Avoid using the i18n filter and the i18n service injected in controllers, directives, services.

AngularJS wrapper has 4 entities: translation provider, service, directive and filter. Both the directive and the filter use the translation service with i18n engine under the hood.

The translation provider is used for service configuration and has the following methods:

addMessages(messages: Map<string, string>, [locale: string]) - provides a way to register translations with the library
setLocale(locale: string) - tells the library which language to use by given language key
getLocale() - returns the current locale
setDefaultLocale(locale: string) - tells the library which language to fallback when missing translations
getDefaultLocale() - returns the default locale
setFormats(formats: object) - supplies a set of options to the underlying formatter
getFormats() - returns current formats
getRegisteredLocales() - returns array of locales having translations
init(messages: Map<string, string>) - initializes the engine

The translation service provides only one method:

i18n(id: string, { values: object, defaultMessage: string, description: string }) – translate message by id

The translation filter is used for attributes translation and has the following syntax:

{{ ::'translationId' | i18n: { values: object, defaultMessage: string, description: string } }}

Where:

translationId - translation id to be translated
values - values to pass into translation
defaultMessage - will be used unless translation was successful (the final fallback in english, will be used for generating en.json)
description - optional context comment that will be extracted by i18n tools and added as a comment next to translation message at defaultMessages.json

The translation directive has the following syntax:

<ANY
  i18n-id="{string}"
  i18n-default-message="{string}"
  [i18n-values="{object}"]
  [i18n-description="{string}"]
></ANY>

Where:

i18n-id - translation id to be translated
i18n-default-message - will be used unless translation was successful
i18n-values - values to pass into translation
i18n-description - optional context comment that will be extracted by i18n tools and added as a comment next to translation message at defaultMessages.json

If HTML rendering in i18n-values is required then value key in i18n-values object should have html_ prefix. Otherwise the value will be inserted to the message without HTML rendering.
Example:

<p
  i18n-id="namespace.id"
  i18n-default-message="Text with an emphasized {text}."
  i18n-values="{
    html_text: '<em>text</em>',
  }"
></p>

Angular I18n module is placed into autoload module, so it will be loaded automatically. After that we can use i18n directive in Angular templates:

<span
  i18n-id="welcome"
  i18n-default-message="Hello!"
></span>

In order to translate attributes in AngularJS we should use i18nFilter:

<input
  type="text"
  placeholder="{{ ::'kbn.management.objects.searchAriaLabel' | i18n: {
    defaultMessage: 'Search { title } Object',
    values: { title }
  } }}"
>

I18n tools

In order to simplify localization process, some additional tools were implemented:

tool for verifying all translations have translatable strings and extracting default messages from templates
tool for verifying translation files and integrating them to Kibana

I18n tools documentation

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I18n

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Attributes translation in React

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I18n tools

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I18n

Localization files

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I18n engine internals

Vanilla JS

React

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Attributes translation in React

AngularJS

I18n tools