I18n Guideline

All Localizers need to know

Message types

The message ids chosen for message keys are descriptive of the string, and its role in the interface (button, label, header, etc.). Each message id ends with a descriptive type. Types are defined at the end of message id by combining to the last segment using camel case.

Ids should end with:

Description (in most cases if it's <p> tag),
Title (if it's <h1>, <h2>, etc. tags),
Label (if it's <label> tag),
ButtonLabel (if it's <button> tag),
DropDownOptionLabel (if it'a an option),
Placeholder (if it's a placeholder),
Tooltip (if it's a tootltip),
AriaLabel (if it's aria-label tag attribute),
ErrorMessage (if it's an error message),
LinkText (if it's <a> tag),
ToggleSwitch and etc.

There is one more complex case, when we have to divide a single expression into different labels.

For example the message before translation looks like:

<p>
    The following deprecated languages are in use: {deprecatedLangsInUse.join(', ')}. Support for these languages will be removed in the next major version of Kibana and Elasticsearch. Convert your scripted fields to <EuiLink href={painlessDocLink}>Painless</EuiLink> to avoid any problems.
</p>

This phrase contains a variable, which represents languages list, and a link (Painless). For such cases we divide the message into two parts: the main message, which contains placeholders, and additional message, which represents inner message.

It is used the following message id naming structure:

the main message id has the type on the penultimate position, thereby identifying a divided phrase, and the last segment ends with Detail.

{
  'kbn.management.editIndexPattern.scripted.deprecationLangLabel.deprecationLangDetail': 'The following deprecated languages are in use: {deprecatedLangsInUse}. Support for these languages will be removed in the next major version of Kibana and Elasticsearch. Convert your scripted fields to {link} to avoid any problems.'
}

The inner message id has the type on the penultimate position and the name of the variable from the placeholder in the main message (in this case link) as the last segment that ends with own type.

For example:

{
  'kbn.management.editIndexPattern.scripted.deprecationLangLabel.painlessLinkLabel': 'Painless'
}

Attribute with variables interpolation

Messages can contain placeholders for embedding a value of a variable. For example:

{
  'kbn.management.editIndexPattern.scripted.deleteFieldLabel': "Delete scripted field '{fieldName}'?"
  'kbn.management.editIndexPattern.scripted.noFieldLabel': "'{indexPatternTitle}' index pattern doesn't have a scripted field called '{fieldName}'"
}

Mostly such placeholders have meaningful name according to the content.

Pluralization

I18n engine supports proper plural forms. It uses the ICU Message syntax to define a message that has a plural label and works for all CLDR languages which have pluralization rules defined. The numeric input is mapped to a plural category, some subset of "zero", "one", "two", "few", "many", and "other" depending on the locale and the type of plural.

For example:

{
  'kbn.management.createIndexPattern.step.status.successLabel.strongIndicesLabel': '{indicesLength, plural, one {# index} other {# indices}}'
}

In case when indicesLength has value 1, the result string will be "1 index". In case when indicesLength has value 2 and more, the result string - "2 indices".

Best practices

Usage of appropriate component

In ReactJS

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 use i18n.translate() instead.

You should use <FormattedMessage> most of the time.
In the case where the string is expected (aria-label, placeholder), Call JS function i18n.translate() from the@kbn/i18n package.

Currently, we support the following ReactJS i18n tools, but they will be removed in future releases:

Usage of props.intl.formatmessage() (where intl is passed to props by injectI18n HOC).

In 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.

Call JS function i18n.translate() from the @kbn/i18n package.
Use i18nId directive in template.

Currently, we support the following AngluarJS i18n tools, but they will be removed in future releases:

Usage of i18n service in controllers, directives, services by injecting it.
Usage of i18n filter in template for attribute translation. Note: Use one-time binding ("{{:: ... }}") in filters wherever it's possible to prevent unnecessary expression re-evaluation.

In JavaScript

Use i18n.translate() in NodeJS or any other framework agnostic code, where i18n is the I18n engine from @kbn/i18n package.

Naming convention

The message ids chosen for message keys should always be descriptive of the string, and its role in the interface (button label, title, etc.). Think of them as long variable names. When you have to change a message id, adding a progressive number to the existing key should always be used as a last resort. Here's a rule of id maning:

{plugin}.{area}.[{sub-area}].{element}

Message id should start with namespace that identifies a functional area of the app (common.ui or common.server) or a plugin (kbn, vega, etc.).

For example:
```
'kbn.management.createIndexPattern.stepTime.options.patternHeader'
'common.ui.indexPattern.warningLabel'
```
Use camelCase for naming segments, comprising several words.

Each message id should end with a type. For example:

'kbn.management.editIndexPattern.createIndexButtonLabel'
'kbn.management.editIndexPattern.mappingConflictTitle'
'kbn.management.editIndexPattern.mappingConflictLabel'
'kbn.management.editIndexPattern.fields.filterAriaLabel'
'kbn.management.editIndexPattern.fields.filterPlaceholder'
'kbn.management.editIndexPattern.refreshTooltip'
'kbn.management.editIndexPattern.fields.allTypesDropDown'
'kbn.management.createIndexPattern.includeSystemIndicesToggleSwitch'
'kbn.management.editIndexPattern.wrongTypeErrorMessage'
'kbn.management.editIndexPattern.scripted.table.nameDescription'

For complex messages, which are divided into several parts, use the following approach:

the main message id should have the type on the penultimate position, thereby identifying a divided phrase, and the last segment should end with Detail,
the inner message id should have the type on the penultimate position and the name of the variable from the placeholder in the main message as the last segment that ends with its own type.

For example, before the translation there was a message:

<strong>Success!</strong>
Your index pattern matches <strong>{exactMatchedIndices.length} {exactMatchedIndices.length === 1 ? 'index' : 'indices'}</strong>.

After translation we get the following structure:

<FormattedMessage
  id="kbn.management.createIndexPattern.step.status.successLabel.successDetail"
  defaultMessage="{strongSuccess} Your index pattern matches {strongIndices}."
  values={{
    strongSuccess: (
      <strong>
        <FormattedMessage
          id="kbn.management.createIndexPattern.step.status.successLabel.strongSuccessLabel"
          defaultMessage="Success!"
        />
      </strong>),
    strongIndices: (
      <strong>
        <FormattedMessage
          id="kbn.management.createIndexPattern.step.status.successLabel.strongIndicesLabel"
          defaultMessage="{indicesLength, plural, one {# index} other {# indices}}"
          values={{ indicesLength: exactMatchedIndices.length }}
        />
      </strong>)
  }}
/>

Defining type for message

Each message id should end with a type of the message.

type	example message id
header	`kbn.management.createIndexPatternTitle`
label	`kbn.management.createIndexPatternLabel`
button	`kbn.management.editIndexPattern.scripted.addFieldButtonLabel`
drop down	`kbn.management.editIndexPattern.fields.allTypesDropDown`
placeholder	`kbn.management.createIndexPattern.stepTime.options.patternPlaceholder`
`aria-label` attribute	`kbn.management.editIndexPattern.removeAriaLabel`
tooltip	`kbn.management.editIndexPattern.removeTooltip`
error message	`kbn.management.createIndexPattern.step.invalidCharactersErrorMessage`
toggleSwitch	`kbn.management.createIndexPattern.includeSystemIndicesToggleSwitch`

For example:

for header:

<h1>
    <FormattedMessage
      id="kbn.management.createIndexPatternTitle"
      defaultMessage="Create index pattern"
    />
</h1>

for label:

<EuiTextColor color="subdued">
    <FormattedMessage
      id="kbn.management.createIndexPatternLabel"
      defaultMessage="Kibana uses index patterns to retrieve data from Elasticsearch indices for things like visualizations."
    />
</EuiTextColor>

for button:

<EuiButton data-test-subj="addScriptedFieldLink" href={addScriptedFieldUrl}>
     <FormattedMessage id="kbn.management.editIndexPattern.scripted.addFieldButtonLabel" defaultMessage="Add scripted field"/>
</EuiButton>

for dropDown:

<select ng-model="indexedFieldTypeFilter" ng-options="o for o in indexedFieldTypes">
    <option value=""
        i18n-id="kbn.management.editIndexPattern.fields.allTypesDropDown"
        i18n-default-message="All field types"></option>
</select>

for placeholder:

<EuiFieldText
    name="indexPatternId"
    placeholder={intl.formatMessage({
      id: 'kbn.management.createIndexPattern.stepTime.options.patternPlaceholder',
      defaultMessage: 'custom-index-pattern-id' })}
/>

for aria-label attribute and tooltip

<button
    aria-label="{{ ::'kbn.management.editIndexPattern.removeAriaLabel' | i18n: {defaultMessage: 'Remove index pattern'} }}"
    tooltip="{{ ::'kbn.management.editIndexPattern.removeTooltip' | i18n: {defaultMessage: 'Remove index pattern'} }}"
    >
</button>

for errorMessage:

errors.push(
    intl.formatMessage(
            {
                id: 'kbn.management.createIndexPattern.step.invalidCharactersErrorMessage',
                defaultMessage: 'An index pattern cannot contain spaces or the characters: {characterList}'
            },
            { characterList }
    ));

for toggleSwitch

<EuiSwitch
    label={<FormattedMessage
      id="kbn.management.createIndexPattern.includeSystemIndicesToggleSwitch"
      defaultMessage="Include system indices"
    />}
/>

Variety of `values`

Variables

<span i18n-id="kbn.management.editIndexPattern.timeFilterHeader"
  i18n-default-message="Time Filter field name: {timeFieldName}"
  i18n-values="{ timeFieldName: indexPattern.timeFieldName }"></span>

<FormattedMessage
  id="kbn.management.createIndexPatternHeader"
  defaultMessage="Create {indexPatternName}"
  values={{
    indexPatternName
  }}
/>

Labels and variables in tag

<span i18n-id="kbn.management.editIndexPattern.timeFilterLabel.timeFilterDetail"
  i18n-default-message="This page lists every field in the {indexPatternTitle} index"
  i18n-values="{ indexPatternTitle: '<strong>' + indexPattern.title + '</strong>' }"></span>

BUT we can not use tags that should be compiled:

<span i18n-id="kbn.management.editIndexPattern.timeFilterLabel.timeFilterDetail"
  i18n-default-message="This page lists every field in the {indexPatternTitle} index"
  i18n-values="{ indexPatternTitle: '<div my-directive>' + indexPattern.title + '</div>' }"></span>

To void injections vulnerability, i18nId directive doesn't compile its values.

<FormattedMessage
  id="kbn.management.createIndexPattern.step.indexPattern.disallowLabel"
  defaultMessage="You can't use spaces or the characters {characterList}."
  values={{ characterList: <strong>{characterList}</strong> }}
/>

<FormattedMessage
  id="kbn.management.settings.form.noSearchResultText"
  defaultMessage="No settings found {clearSearch}"
  values={{
    clearSearch: (
      <EuiLink onClick={clearQuery}>
        <FormattedMessage
          id="kbn.management.settings.form.clearNoSearchResultText"
          defaultMessage="(clear search)"
        />
      </EuiLink>
    ),
  }}
/>

Non-translatable text such as property name.

<FormattedMessage
  id="xpack.security.management.users.editUser.changePasswordUpdateKibanaTitle"
  defaultMessage="After you change the password for the kibana user, you must update the {kibana}
  file and restart Kibana."
  values={{ kibana: 'kibana.yml' }}
/>

Text with plurals

The numeric input is mapped to a plural category, some subset of "zero", "one", "two", "few", "many", and "other" depending on the locale and the type of plural. There are languages with multiple plural forms Language Plural Rules.

Here is an example of message translation depending on a plural category:

<span i18n-id="kbn.management.editIndexPattern.mappingConflictLabel"
      i18n-default-message="{conflictFieldsLength, plural, one {A field is} other {# fields are}} defined as several types (string, integer, etc) across the indices that match this pattern."
      i18n-values="{ conflictFieldsLength: conflictFields.length }"></span>

When conflictFieldsLength equals 1, the result string will be "A field is defined as several types (string, integer, etc) across the indices that match this pattern.". In cases when conflictFieldsLength has value of 2 or more, the result string - "2 fields are defined as several types (string, integer, etc) across the indices that match this pattern.".

Splitting

Splitting sentences into several keys often inadvertently presumes a grammar, a sentence structure, and such composite strings are often very difficult to translate.

Do not divide a single sentence into different labels unless you have absolutely no other choice.
Do not divide sentences that belong together into separate labels.

For example:

The following dialogue box indicates progress. You can close it and the process will continue to run in the background.

If this group of sentences is separated it’s possible that the context of the 'it' in 'close it' will be lost.

Unit tests

Testing React component that uses the injectI18n higher-order component is more complicated because injectI18n() creates a wrapper component around the original component.

With shallow rendering only top level component is rendered, that is a wrapper itself, not the original component. Since we want to test the rendering of the original component, we need to access it via the wrapper's WrappedComponent property. Its value will be the component we passed into injectI18n().

When testing such component, use the shallowWithIntl helper function defined in test_utils/enzyme_helpers and pass the component's WrappedComponent property to render the wrapped component. This will shallow render the component with Enzyme and inject the necessary context and props to use the intl mock defined in test_utils/mocks/intl.

Use the mountWithIntl helper function to mount render the component.

For example, there is a component that is wrapped by injectI18n, like in the AddFilter component:

// ...
export const AddFilter = injectI18n(
  class AddFilterUi extends Component {
  // ...
    render() {
      const { filter } = this.state;
      return (
        <EuiFlexGroup>
          <EuiFlexItem grow={10}>
            <EuiFieldText
              fullWidth
              value={filter}
              onChange={e => this.setState({ filter: e.target.value.trim() })}
              placeholder={this.props.intl.formatMessage({
                id: 'kbn.management.indexPattern.edit.source.placeholder',
                defaultMessage: 'source filter, accepts wildcards (e.g., `user*` to filter fields starting with \'user\')'
              })}
            />
          </EuiFlexItem>
        </EuiFlexGroup>
      );
    }
  }
);

To test the AddFilter component it is needed to render its WrappedComponent property using shallowWithIntl function to pass intl object into the props.

// ...
it('should render normally', async () => {
    const component = shallowWithIntl(
      <AddFilter.WrappedComponent onAddFilter={() => {}}/>
    );

    expect(component).toMatchSnapshot();
});
// ...

Development steps

Localize label with the suitable i18n component.
Make sure that UI still looks correct and is functioning properly (e.g. click handler is processed, checkbox is checked/unchecked, etc.).
Check functionality of an element (button is clicked, checkbox is checked/unchecked, etc.).

Run i18n validation/extraction tools and skim through created en.json:

$ node scripts/i18n_check --ignore-missing
$ node scripts/i18n_extract --output-dir ./

Run linters and type checker as you normally do.
Run tests.
Run Kibana with enabled pseudo-locale (either pass --i18n.locale=en-xa as a command-line argument or add it to the kibana.yml) and observe the text you've just localized.

If you did everything correctly, it should turn into something like this Ĥéļļļô ŴŴôŕļļð! assuming your text was Hello World!.
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GUIDELINE.md

GUIDELINE.md

I18n Guideline

All Localizers need to know

Message types

Attribute with variables interpolation

Pluralization

Best practices

Usage of appropriate component

In ReactJS

In AngularJS

In JavaScript

Naming convention

Defining type for message

Variety of `values`

Text with plurals

Splitting

Unit tests

Development steps

Files

GUIDELINE.md

Latest commit

History

GUIDELINE.md

File metadata and controls

I18n Guideline

All Localizers need to know

Message types

Attribute with variables interpolation

Pluralization

Best practices

Usage of appropriate component

In ReactJS

In AngularJS

In JavaScript

Naming convention

Defining type for message

Variety of values

Text with plurals

Splitting

Unit tests

Development steps

Variety of `values`