> For the complete documentation index, see [llms.txt](https://help.bots.business/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.bots.business/libraries-and-examples/language.md).

# Translate bot messages with Lang

Configure message dictionaries and let each bot user choose a language with the Lang library.

Install `Lang` to store message dictionaries and a language choice for each bot user. It does not translate text automatically. Supply the translations you want the bot to send.

{% stepper %}
{% step %}

### Configure two languages

Run this once from an owner-only setup command:

{% code title="Configure two languages · Example 1" overflow="wrap" %}

```javascript
Libs.Lang.setup("en", {
  greeting: "Hello!",
  account: { empty: "No saved details yet." }
});
Libs.Lang.setup("es", {
  greeting: "¡Hola!",
  account: { empty: "Todavía no hay datos guardados." }
});
Libs.Lang.default.setLang("en");
```

{% endcode %}

The first configured language becomes the default unless you explicitly change it. Re-running setup replaces the dictionary stored under that language name, so include all its keys.

In `/hello`:

{% code title="Configure two languages · Example 2" overflow="wrap" %}

```javascript
Bot.sendMessage(Libs.Lang.t("greeting"));
Bot.sendMessage(Libs.Lang.t("account.empty"));
```

{% endcode %}

Keys such as `account.empty` are paths in your own dictionary. Keep them fixed in your code; do not pass arbitrary user text as a translation expression.
{% endstep %}

{% step %}

### Let a user choose

In `/english`:

{% code title="Let a user choose · Example 3" overflow="wrap" %}

```javascript
Libs.Lang.user.setLang("en");
Bot.sendMessage(Libs.Lang.t("greeting"));
```

{% endcode %}

In `/spanish`, use `Libs.Lang.user.setLang("es")`. Configure the dictionary before letting users select it. A selected language with no configured dictionary raises an error.
{% endstep %}
{% endstepper %}

## Reference

| Call                                          | Result                                             |
| --------------------------------------------- | -------------------------------------------------- |
| `Libs.Lang.user.getCurLang()`                 | User's selected language, or default               |
| `Libs.Lang.default.getCurLang()`              | Bot's default language                             |
| `Libs.Lang.get("en")`                         | Full dictionary for that language                  |
| `Libs.Lang.t("key", "en")`                    | Translation in an explicitly selected language     |
| `Libs.Lang.getCommandByAlias(text, language)` | Matching command name from an `aliases` dictionary |

`t()` falls back to the default language for a missing or falsy value. Use nonempty message strings; an empty string, `false` or numeric zero is not a reliable translation value for this fallback behavior.

An aliases dictionary can map visible labels to commands:

{% code title="Reference · Example 4" overflow="wrap" %}

```javascript
Libs.Lang.setup("en", {
  greeting: "Hello!",
  aliases: { "Help, Support": "/help" }
});
```

{% endcode %}

`getCommandByAlias` performs a case insensitive lookup. It returns a name; your code decides whether to run it. Translation keys and BJS method names stay unchanged across languages.

If you need whole reply layouts with buttons and placeholders, use [SmartBot templates](/libraries-and-examples/smart-bot.md). Its language storage is separate from `Libs.Lang`.