video.js/docs/guides/languages.md

# Languages
Multiple language support allows for users of non-English locales to natively interact with the Video.js player.

For an up-to-date list of the languages Video.js supports, see the [languages folder (`lang`)][lang-supported]. These JSON files are converted to JavaScript during the Video.js build process.

## Using Video.js Languages
Video.js ships with multiple translations (in `dist/lang/`) in JavaScript files. Each of these files can be included in a web page to provide support for that language in _all_ Video.js players:

```
<script src="//example.com/path/to/video.min.js"></script>
<script src="//example.com/path/to/lang/es.js"></script>
```

## Contributing to Video.js Translations
We welcome new translations and improvements to existing ones! Please see the [contributing document](../../CONTRIBUTING.md) to get started contributing to Video.js and continue reading for specifics on how to contribute to translations of Video.js...

### JSON Format
Video.js uses a JSON object to describe a language, where the keys are English and the values are the target language. For example, a Spanish translation might look like this:

```JSON
{
  "Play": "Reproducción",
  "Pause": "Pausa",
  "Current Time": "Tiempo reproducido",
  "Duration Time": "Duración total",
  "Remaining Time": "Tiempo restante",
  ...
}
```

### File Naming
Translations are always found in the `lang/` directory.

Each file's name should be the [standard language code][lang-codes] that is most appropriate. For example, "es" for Spanish or "zh-CN" for Chinese.

Finally, each file's extension is always `.json`.

### Updating an Existing Translation

If there is a [missing translation](../translations-needed.md), mistake, or room for improvement in an existing translation, don't hesitate to open a pull request!

1. Edit the relevant JSON file and make the necessary changes.
1. Verify the language compiles by running `grunt dist`.
1. Verify the translation appears properly in the player UI.
1. Run `grunt check-translations` to update the [missing translation document](../translations-needed.md).
1. Commit and open a pull request on GitHub.

### Writing a New Translation
The process for writing an entirely new translation is virtually identical to the process for [updating an existing translation](#updating-an-existing-translation) except that the new translation JSON file needs to be created.

The template for new language files is the English file ([lang/en.json][lang-en]). This file is always up-to-date with strings that need translations.

The first step to writing a new translation is to copy the English file:

```sh
$ cp lang/en.json lang/${NEW_LANG_CODE}.json
```

Otherwise, the process is the same as [updating an existing translation](#updating-an-existing-translation).

## Advanced Language Usage
The instructions above for [using Video.js languages](#using-videojs-languages) should be sufficient for the majority of use-cases. However, languages can be provided at runtime.

In each case, these custom language definitions _take precedence over any Video.js-provided languages!_

### Adding Languages via the API
In addition to the stand-alone scripts provided by Video.js, the API supports manual definition of new languages via the `addLanguage` method. It takes two arguments: the [standard language code][lang-codes] and a [language definition object](#json-format).

```js
videojs.addLanguage('es', {
  'Play': 'Reproducción',
  'Pause': 'Pausa',
  'Current Time': 'Tiempo reproducido',
  'Duration Time': 'Duración total',
  'Remaining Time': 'Tiempo restante',
  ...
});
```

### Per-Player Languages
In addition to providing languages to Video.js itself, individual `Player` instances can be provided custom language support via [the `languages` option](options.md#languages):

```js
// Provide a custom definition of Spanish to this player.
videojs('my-player', {
  languages: {
    es: {...}
  }
});
```

### Setting Default Player Language

Player instances can also have a default language via [the `language` option](options.md#language):

```js
// Set the default language to Spanish for this player.
videojs('my-player', {
  language: 'es'
});
```

Additionally, the `language` method of the player can be used to set the language after instantiation (e.g., `language('es')`). However, this is not recommended as it does not update the UI in place. _Setting the language via options is always preferred._

### Determining Player Language

The player language is set to one of the following in descending priority:

- The language [specified in options](#setting-default-player-language)
- The language specified by the closest element with a `lang` attribute. This could be the player itself or a parent element. Usually, the document language is specified on the `<html>` tag.
- Browser language preference; the first language if more than one is configured
- English

#### Internal Language Selection
- Language codes are considered case-insensitively (e.g. `en-US` == `en-us`).
- If there is no match for a language code with a subcode (e.g. `en-us`), a match for the primary code (e.g. `en`) is used if available.

## References

For information on translation/localization in plugins, see [the plugins guide](plugins.md).

Standard languages codes [are defined by the IANA][lang-codes].

For all existing/supported languages, please see the [languages lolder (`lang/`)][lang-supported] folder located in the project root.


[lang-en]: https://github.com/videojs/video.js/tree/master/lang/en.json
[lang-supported]: https://github.com/videojs/video.js/tree/master/lang
[lang-codes]: http://www.iana.org/assignments/language-subtag-registry/language-subtag-registry