angular-cn/aio/content/guide/i18n.md

Internationalization (i18n)

Application internationalization is a many-faceted area of development, focused on making applications available and user-friendly to a worldwide audience. This page describes Angular's internationalization (i18n) tools, which can help you make your app available in multiple languages.

See the i18n Example for a simple example of an AOT-compiled app, translated into French.

可以把这个翻译为法语版的 AOT 应用i18n 例子作为一个简单的例子。

{@a angular-i18n}

Angular and i18n

Angular simplifies the following aspects of internationalization:

• Displaying dates, number, percentages, and currencies in a local format.

• Translating text in component templates.

• Handling plural forms of words.

• Handling alternative text.

This document focuses on Angular CLI projects, in which the Angular CLI generates most of the boilerplate necessary to write your app in multiple languages.

{@a setting-up-locale}

Setting up the locale of your app

A locale is an identifier (id) that refers to a set of user preferences that tend to be shared within a region of the world, such as country. This document refers to a locale identifier as a "locale" or "locale id".

A Unicode locale identifier is composed of a Unicode language identifier and (optionally) the character - followed by a locale extension. (For historical reasons the character _ is supported as an alternative to -.) For example, in the locale id fr-CA the fr refers to the French language identifier, and the CA refers to the locale extension Canada.

Angular follows the Unicode LDML convention that uses stable identifiers (Unicode locale identifiers) based on the norm BCP47. It is very important that you follow this convention when you define your locale, because the Angular i18n tools use this locale id to find the correct corresponding locale data.

国际化工作者通常将一个可翻译的文本叫作“信息”。 本章使用了“文本”和“信息”，它们可以互换，也可以组合“文本信息”。

By default, Angular uses the locale en-US, which is English as spoken in the United States of America.

To set your app's locale to another value, use the CLI parameter --locale with the value of the locale id that you want to use:

ng serve --aot --locale fr

If you use JIT, you also need to define the LOCALE_ID provider in your main module:

For more information about Unicode locale identifiers, see the CLDR core spec.

For a complete list of locales supported by Angular, see the Angular repository.

The locale identifiers used by CLDR and Angular are based on BCP47. These specifications change over time; the following table maps previous identifiers to current ones at time of writing:

Locale name	Old locale id	New locale id
Indonesian	in	id
Hebrew	iw	he
Romanian Moldova	mo	ro-MD
Norwegian Bokmål	no, no-NO	nb
Serbian Latin	sh	sr-Latn
Filipino	tl	fil
Portuguese Brazil	pt-BR	pt
Chinese Simplified	zh-cn, zh-Hans-CN	zh-Hans
Chinese Traditional	zh-tw, zh-Hant-TW	zh-Hant
Chinese Traditional Hong Kong	zh-hk	zh-Hant-HK

i18n pipes

Angular pipes can help you with internationalization: the DatePipe, CurrencyPipe, DecimalPipe and PercentPipe use locale data to format data based on the LOCALE_ID.

By default, Angular only contains locale data for en-US. If you set the value of LOCALE_ID to another locale, you must import locale data for that new locale. The CLI imports the locale data for you when you use the parameter --locale with ng serve and ng build.

If you want to import locale data for other languages, you can do it manually:

The first parameter is an object containing the locale data imported from @angular/common/locales. By default, the imported locale data is registered with the locale id that is defined in the Angular locale data itself. If you want to register the imported locale data with another locale id, use the second parameter to specify a custom locale id. For example, Angular's locale data defines the locale id for French as "fr". You can use the second parameter to associate the imported French locale data with the custom locale id "fr-FR" instead of "fr".

The files in @angular/common/locales contain most of the locale data that you need, but some advanced formatting options might only be available in the extra dataset that you can import from @angular/common/locales/extra. An error message informs you when this is the case.

All locale data used by Angular are extracted from the Unicode Consortium's Common Locale Data Repository (CLDR).

Template translations

This document refers to a unit of translatable text as "text," a "message", or a "text message."

The i18n template translation process has four phases:

1. Mark static text messages in your component templates for translation.

2. An Angular i18n tool extracts the marked text into an industry standard translation source file.

3. A translator edits that file, translating the extracted text into the target language, and returns the file to you.

4. The Angular compiler imports the completed translation files, replaces the original messages with translated text, and generates a new version of the app in the target language.

You need to build and deploy a separate version of the app for each supported language.

{@a i18n-attribute}

Mark text with the i18n attribute

The Angular i18n attribute marks translatable content. Place it on every element tag whose fixed text is to be translated.

In the example below, an <h1> tag displays a simple English language greeting, "Hello i18n!"

To mark the greeting for translation, add the i18n attribute to the <h1> tag.

添加i18n属性到该标签上，把它标记为需要翻译的文本。

i18n is a custom attribute, recognized by Angular tools and compilers. After translation, the compiler removes it. It is not an Angular directive.

{@a help-translator}

Help the translator with a description and meaning

To translate a text message accurately, the translator may need additional information or context.

You can add a description of the text message as the value of the i18n attribute, as shown in the example below:

The translator may also need to know the meaning or intent of the text message within this particular app context.

为了给出正确的翻译，翻译者需要知道你这段文本在特定情境下的 真实意图。

You add context by beginning the i18n attribute value with the meaning and separating it from the description with the | character: <meaning>|<description>

在描述的前面，我们为指定的字符串添加一些上下文含义，用|将其与描述文字隔开(<意图>|<描述>)。

All occurrences of a text message that have the same meaning will have the same translation. A text message that is associated with different meanings can have different translations.

The Angular extraction tool preserves both the meaning and the description in the translation source file to facilitate contextually-specific translations, but only the combination of meaning and text message are used to generate the specific id of a translation. If you have two similar text messages with different meanings, they are extracted separately. If you have two similar text messages with different descriptions (not different meanings), then they are extracted only once.

如果所有地方出现的文本具有相同含义时，它们应该有相同的翻译， 但是如果在某些地方它具有不同含义，那么它应该有不同的翻译。 Angular的提取工具在翻译源文件中保留含义和描述，以支持符合特定上下文的翻译。

{@a custom-id}

Set a custom id for persistence and maintenance

设置一个自定义的id来提升可搜索性和可维护性

The angular i18n extractor tool generates a file with a translation unit entry for each i18n attribute in a template. By default, it assigns each translation unit a unique id such as this one:

Angular 的 i18n 提取工具会为模板中每个带有i18n属性的元素生成一个*翻译单元（translation unit）*条目，并保存到一个文件中。默认情况下，它为每个翻译单元指定一个唯一的id，就像这样：

When you change the translatable text, the extractor tool generates a new id for that translation unit. You must then update the translation file with the new id.

当我们修改这段可翻译的文字时，提取工具会为那个翻译单元生成一个新的id。 我们就要使用这个新的 id 来修改这个翻译文件。

Alternatively, you can specify a custom id in the i18n attribute by using the prefix @@. The example below defines the custom id introductionHeader:

When you specify a custom id, the extractor tool and compiler generate a translation unit with that custom id.

现在，提取工具和编译器就会用*你的自定义id`生成一个翻译单元，而不会再改变它。

The custom id is persistent. The extractor tool does not change it when the translatable text changes. Therefore, you do not need to update the translation. This approach makes maintenance easier.

Use a custom id with a description

You can use a custom id in combination with a description by including both in the value of the i18n attribute. In the example below, the i18n attribute value includes a description, followed by the custom id:

You also can add a meaning, as shown in this example:

下面这个例子带有含义和描述，最后是id：

Define unique custom ids

Be sure to define custom ids that are unique. If you use the same id for two different text messages, only the first one is extracted, and its translation is used in place of both original text messages.

为了确保定义出唯一的自定义id。如果我们对两个不同的文本块使用了同一个id，那么就只有一个会被提取出来，然后其翻译结果会被用于全部文本块。

In the example below the custom id myId is used for two different messages:

  <h3 i18n="@@myId">Hello</h3>

  <!-- ... -->

  <p i18n="@@myId">Good bye</p>

Consider this translation to French:

  <trans-unit id="myId" datatype="html">
    <source>Hello</source>
    <target state="new">Bonjour</target>
  </trans-unit>

Because the custom id is the same, both of the elements in the resulting translation contain the same text, Bonjour:

  <h3>Bonjour</h3>

  <!-- ... -->

  <p>Bonjour</p>

{@a no-element}

Translate text without creating an element

翻译文本，而不必创建元素

If there is a section of text that you would like to translate, you can wrap it in a <span> tag. However, if you don't want to create a new DOM element merely to facilitate translation, you can wrap the text in an <ng-container> element. The <ng-container> is transformed into an html comment:

如果要翻译一段纯文本，我们就可以把它用<span>标签包裹起来。 但如果由于某些原因（比如CSS结构方面的考虑），我们可能不希望仅仅为了翻译而创建一个新的DOM元素，那么也可以把这段文本包裹进一个<ng-container>元素中。<ng-container>将被转换成一个HTML注释：

{@a translate-attributes}

Add i18n translation attributes

添加 i18n 翻译属性

You also can translate attributes. For example, assume that your template has an image with a title attribute:

我们还可以翻译属性。 比如，假设我们的模板具有一个带title属性的图片：

This title attribute needs to be translated.

这个 title 属性也需要翻译。

To mark an attribute for translation, add an attribute in the form of i18n-x, where x is the name of the attribute to translate. The following example shows how to mark the title attribute for translation by adding the i18n-title attribute on the img tag:

This technique works for any attribute of any element.

You also can assign a meaning, description, and id with the i18n-x="<meaning>|<description>@@<id>" syntax.

我们也同样可以使用i18n-x="<meaning>|<description>@@<id>"语法来指定一个含义和描述。

{@a plural-ICU}

Translate singular and plural

处理单数与复数

Different languages have different pluralization rules.

不同的语言有不同的单复数规则。

Suppose that you want to say that something was "updated x minutes ago". In English, depending upon the number of minutes, you could display "just now", "one minute ago", or "x minutes ago" (with x being the actual number). Other languages might express the cardinality differently.

假设应用中需要谈论一些狼。 在英语中，根据狼的数量，可能要显示为"no wolves"、"one wolf"、"two wolves"或"a wolf pack"。 而在其它语言中则可能会有不同的基数规则。

The example below shows how to use a plural ICU expression to display one of those three options based on when the update occurred:

• The first parameter is the key. It is bound to the component property (minutes), which determines the number of minutes.

  第一个参数是key。它绑定到了组件中表示狼的数量的wolves属性。

• The second parameter identifies this as a plural translation type.

  第二个参数表示这是一个plural（复数）翻译类型。

• The third parameter defines a pluralization pattern consisting of pluralization categories and their matching values.

  第三个参数定义了一组复数表示模式，这个模式由复数类别和它们所匹配的值组成。

This syntax conforms to the ICU Message Format as specified in the CLDR pluralization rules.

Pluralization categories include (depending on the language):

复数类别包括（取决于语言）：

• =0 (or any other number)

  =0 （或其它数字）

• zero

  zero（零）

• one

  one（一个)

• two

  two（两个）

• few

  few（少数）

• many

  many（很多）

• other

After the pluralization category, put the default English text in braces ({}).

把默认的英语翻译结果放在复数类别之后的括号（{}）中。

In the example above, the three options are specified according to that pluralization pattern. For talking about about zero minutes, you use =0 {just now}. For one minute, you use =1 {one minute}. Any unmatched cardinality uses other {{{minutes}} minutes ago}. You could choose to add patterns for two, three, or any other number if the pluralization rules were different. For the example of "minute", only these three patterns are necessary in English.

You can use interpolations and html markup inside of your translations.

{@a select-ICU}

Select among alternative text messages

在候选文本中选择

If your template needs to display different text messages depending on the value of a variable, you need to translate all of those alternative text messages.

You can handle this with a select ICU expression. It is similar to the plural ICU expressions except that you choose among alternative translations based on a string value instead of a number, and you define those string values.

The following format message in the component template binds to the component's gender property, which outputs one of the following string values: "m", "f" or "o". The message maps those values to the appropriate translations:

组件模板中的下列消息格式绑定到了组件的gender属性，这个属性的取值是 "m" 或 "f" 或 "o"。 这个消息会把那些值映射到适当的翻译文本：

{@a nesting-ICUS}

Nesting plural and select ICU expressions

把"复数"与"选择"表达式嵌套在一起

You can also nest different ICU expressions together, as shown in this example:

我们也可以把不同的 ICU 表达式嵌套在一起，比如：

{@a ng-xi18n}

Create a translation source file with ng xi18n

使用_ng-xi18n_工具创建翻译源文件

Use the ng xi18n command provided by the CLI to extract the text messages marked with i18n into a translation source file.

使用ng-xi18n提取工具来将带i18n标记的文本提取到一个翻译源文件中。

Open a terminal window at the root of the app project and enter the ng xi18n command:

在应用的项目根目录打开一个终端窗口，并输入ng-xi18n命令：

ng xi18n

By default, the tool generates a translation file named messages.xlf in the XML Localization Interchange File Format (XLIFF, version 1.2).

If you don't use the CLI, you have two options:

• You can use the ng-xi18n tool directly from the @angular/compiler-cli package. For more information, see i18n in the CLI documentation.

• You can use the CLI Webpack plugin AngularCompilerPlugin from the @ngtools/webpack package. Set the parameters i18nOutFile and i18nOutFormat to trigger the extraction. For more information, see the Angular Ahead-of-Time Webpack Plugin documentation.

{@a other-formats}

Other translation formats

其它翻译格式

Angular i18n tooling supports three translation formats:

• XLIFF 1.2 (default)

• XLIFF 2

• XML Message Bundle (XMB)

You can specify the translation format explicitly with the --i18nFormat flag as illustrated in these example commands:

我们可以使用--i18nFormat来明确指定想用的格式，范例如下：

ng xi18n --i18nFormat=xlf ng xi18n --i18nFormat=xlf2 ng xi18n --i18nFormat=xmb

The sample in this guide uses the default XLIFF 1.2 format.

XLIFF files have the extension .xlf. The XMB format generates .xmb source files but uses .xtb (XML Translation Bundle: XTB) translation files.

{@a ng-xi18n-options}

Other options

其它选项

You can specify the output path used by the CLI to extract your translation source file with the parameter --outputPath:

我们还可能需要指定其它选项。 比如，如果TypeScript的配置文件tsconfig.json位于其它地方而不是根目录，我们就要通过-p选项来明确指出它的路径。

ng xi18n --outputPath src/locale

You can change the name of the translation source file that is generated by the extraction tool with the parameter --outFile:

ng xi18n --outFile source.xlf

You can specify the base locale of your app with the parameter --locale:

ng xi18n --locale fr

The extraction tool uses the locale to add the app locale information into your translation source file. This information is not used by Angular, but external translation tools may need it.

{@a translate}

Translate text messages

翻译文本信息

The ng xi18n command generates a translation source file named messages.xlf in the project src folder.

ng xi18n命令在项目根目录生成一个名为messages.xlf的翻译源文件。

The next step is to translate this source file into the specific language translation files. The example in this guide creates a French translation file.

下一步是将英文模板文本翻译到指定语言的翻译文件。 这个例子中创建了一个法语翻译文件。

{@a localization-folder}

Create a localization folder

新建一个本土化目录

Most apps are translated into more than one other language. For this reason, it is standard practice for the project structure to reflect the entire internationalization effort.

大多数应用都要被翻译成多种其它语言，因此，为全部国际化工作做适当的调整项目目录结构是一种标准实践。

One approach is to dedicate a folder to localization and store related assets, such as internationalization files, there.

其中一种方法是为本土化和相关资源（比如国际化文件）创建一个专门的目录。

Localization and internationalization are different but closely related terms.

本土化和国际化是不同但是很相近的概念。

This guide follows that approach. It has a locale folder under src/. Assets within that folder have a filename extension that matches their associated locale.

Create the translation files

For each translation source file, there must be at least one language translation file for the resulting translation.

For this example:

1. Make a copy of the messages.xlf file.

2. Put the copy in the locale folder.

3. Rename the copy to messages.fr.xlf for the French language translation.

If you were translating to other languages, you would repeat these steps for each target language.

{@a translate-text-nodes}

Translate text nodes

翻译文本节点

In a large translation project, you would send the messages.fr.xlf file to a French translator who would enter the translations using an XLIFF file editor.

在现实世界中，messages.fr.xlf文件会被发给法语翻译，他们使用这些XLIFF文件编辑器中的一种来翻译它。

This sample file is easy to translate without a special editor or knowledge of French.

我们不需要任何编辑器或者法语知识就可以轻易的翻译本例子文件。

1. Open messages.fr.xlf and find the first <trans-unit> section:

This XML element represents the translation of the <h1> greeting tag that you marked with the i18n attribute earlier in this guide.

Note that the translation unit id=introductionHeader is derived from the custom id that you set earlier, but without the @@ prefix required in the source HTML.

2. Duplicate the <source/> tag, rename it target, and then replace its content with the French greeting. If you were working with a more complex translation, you could use the the information and context provided by the source, description, and meaning elements to guide your selection of the appropriate French translation.

3. Translate the other text nodes the same way:

The Angular i18n tools generated the ids for these translation units. Don't change them. Each id depends upon the content of the template text and its assigned meaning. If you change either the text or the meaning, then the id changes. For more information, see the translation file maintenance discussion.

{@a translate-plural-select}

Translate plural and select expressions

Plural and select ICU expressions are extracted separately, so they require special attention when preparing for translation.

Look for these expressions in relation to other translation units that you recognize from elsewhere in the source template. In this example, you know the translation unit for the select must be just below the translation unit for the logo.

{@a translate-plural}

Translate plural

To translate a plural, translate its ICU format match values:

要翻译一个复数，就要翻译它的ICU格式中匹配的值：

You can add or remove plural cases, with each language having its own cardinality. (See CLDR plural rules.)

{@a translate-select}

Translate select

翻译选择（select）

Below is the content of our example select ICU expression in the component template:

The extraction tool broke that into two translation units because ICU expressions are extracted separately.

提取工具会把它拆成两个翻译单元，因为 ICU 表达式是分别提取的。

The first unit contains the text that was outside of the select. In place of the select is a placeholder, <x id="ICU">, that represents the select message. Translate the text and move around the placeholder if necessary, but don't remove it. If you remove the placeholder, the ICU expression will not be present in your translated app.

第一个单元包含select之外的文本。 这里的select是一个占位符<x id="ICU">，用来表示select中的消息。 翻译这段文本，并把占位符放在那里。

The second translation unit, immediately below the first one, contains the select message. Translate that as well.

第一个翻译单元的紧下方就是第二个翻译单元，包含select中的消息。翻译它。

Here they are together, after translation:

在翻译之后，它们会放在一起：

{@a translate-nested}

Translate a nested expression

翻译嵌套的表达式

A nested expression is similar to the previous examples. As in the previous example, there are two translation units. The first one contains the text outside of the nested expression:

嵌套的表达式和前一节没有什么不同。就像上一个例子中那样，我们有两个翻译单元。

The second unit contains the complete nested expression:

第二个包含完整的嵌套表达式：

And both together:

放在一起时：

The entire template translation is complete. The next section describes how to load that translation into the app.

{@a app-pre-translation}

The app and its translation file

应用及其翻译文件

The sample app and its translation file are now as follows:

下面是例子应用及其翻译文件：

{@a merge}

Merge the completed translation file into the app

合并已经翻译的文件

To merge the translated text into component templates, compile the app with the completed translation file. Provide the Angular compiler with three translation-specific pieces of information:

• The translation file.

  翻译文件

• The translation file format.

  翻译文件的格式

• The locale (fr or en-US for instance).

The compilation process is the same whether the translation file is in .xlf format or in another format that Angular understands, such as .xtb.

How you provide this information depends upon whether you compile with the JIT compiler or the AOT compiler.

• With AOT, you pass the information as a CLI parameter.

• With JIT, you provide the information at bootstrap time.

{@a merge-aot}

Merge with the AOT compiler

The AOT (Ahead-of-Time) compiler is part of a build process that produces a small, fast, ready-to-run application package.

When you internationalize with the AOT compiler, you must pre-build a separate application package for each language and serve the appropriate package based on either server-side language detection or url parameters.

You also need to instruct the AOT compiler to use your translation file. To do so, you use three options with the ng serve or ng build commands:

• --i18nFile: the path to the translation file.

• --i18nFormat: the format of the translation file.

• --locale: the locale id.

The example below shows how to serve the French language file created in previous sections of this guide:

ng serve --aot --i18nFile=src/locale/messages.fr.xlf --i18nFormat=xlf --locale=fr

{@a merge-jit}

Merge with the JIT compiler

用JiT编译器合并

The JIT compiler compiles the app in the browser as the app loads. Translation with the JIT compiler is a dynamic process of:

JiT（即时）编译器在应用程序加载时，在浏览器中编译应用。 在使用JiT编译器的环境中翻译是一个动态的流程，包括：

1. Importing the appropriate language translation file as a string constant.

   把合适的语言翻译文件导入成一个字符串常量

2. Creating corresponding translation providers for the JIT compiler.

   为JiT编译器创建相应的翻译提供商。

3. Bootstrapping the app with those providers.

   使用这些提供商来启动应用。

Three providers tell the JIT compiler how to translate the template texts for a particular language while compiling the app:

三种提供商帮助JiT编译在编译应用时，将模板文本翻译到某种语言：

• TRANSLATIONS is a string containing the content of the translation file.

  TRANSLATIONS是含有翻译文件内容的字符串。

• TRANSLATIONS_FORMAT is the format of the file: xlf, xlf2, or xtb.

  TRANSLATIONS_FORMAT是文件的格式: xlf、xlif或xtb。

• LOCALE_ID is the locale of the target language.

  LOCALE_ID是目标语言的语言环境。

The Angular bootstrapModule method has a second compilerOptions parameter that can influence the behavior of the compiler. You can use it to provide the translation providers:

在下面的src/app/i18n-providers.ts文件的getTranslationProviders()函数中，根据用户的语言环境和对应的翻译文件构建这些提供商：

Then provide the LOCALE_ID in the main module:

{@a missing-translation}

Report missing translations

By default, when a translation is missing, the build succeeds but generates a warning such as Missing translation for message "foo". You can configure the level of warning that is generated by the Angular compiler:

• Error: throw an error. If you are using AOT compilation, the build will fail. If you are using JIT compilation, the app will fail to load.

• Warning (default): show a 'Missing translation' warning in the console or shell.

• Ignore: do nothing.

If you use the AOT compiler, specify the warning level by using the CLI parameter --missingTranslation. The example below shows how to set the warning level to error:

ng serve --aot --missingTranslation=error

If you use the JIT compiler, specify the warning level in the compiler config at bootstrap by adding the 'MissingTranslationStrategy' property. The example below shows how to set the warning level to error: