docs: added language rule

Author: andrepimpao

docs/03-rules.md

@@ -39,6 +39,7 @@
 
 - [Choice](03-rules_choice.md)
 - [Country](03-rules_country.md)
+- [Language](03-rules_language.md)
 
 ## Iterable Rules
 

docs/03-rules_language.md

@@ -0,0 +1,58 @@
+# Language
+
+Validates that a value is a valid language code.
+
+```php
+Language(
+    string $code = 'alpha-2',
+    ?string $message = null
+);
+```
+
+## Basic Usage
+
+```php
+// default alpha-2 code
+Validator::language()->validate('pt'); // true
+
+// alpha-3 code
+Validator::language(code: 'alpha-3')->validate('por'); // true
+```
+
+> [!NOTE]
+> An `UnexpectedValueException` will be thrown when the `code` value is not a valid option.
+
+> [!NOTE]
+> An `UnexpectedValueException` will be thrown when the input value is not a `string`.
+
+## Options
+
+### `code`
+
+type: `string` default: `alpha-2`
+
+Set code type to validate the language. 
+Check the [official language codes](https://en.wikipedia.org/wiki/List_of_ISO_639_language_codes) list for more information.
+
+Available options:
+
+- `alpha-2`: two-letter code
+- `alpha-3`: three-letter code
+
+### `message`
+
+type: `?string` default: `The {{ name }} value is not a valid language, {{ value }} given.`
+
+Message that will be shown if the input value is not a valid language code.
+
+The following parameters are available:
+
+| Parameter     | Description               |
+|---------------|---------------------------|
+| `{{ value }}` | The current invalid value |
+| `{{ name }}`  | Name of the invalid value |
+| `{{ code }}`  | Selected code type        |
+
+## Changelog
+
+- `1.1.0` Created