Declare your application locales under ~/config/strata.php. You can specify the url key as well as the locale code. It is important that the locale code follows ISO standards. It must have either two characters (en) or be the complete version containing the country information (en_US).

<?php
$strata = array(
    "routes" => array(),
    "custom-post-types" => array(),

    "i18n" => array(
        "textdomain" => "my_website",
        "default_locale_fallback" => true,
        "locales" => array(
            "en_CA" => array("nativeLabel" => "English", "default" => true),
            "fr_CA" => array("nativeLabel" => "Français", "url" => "francais"),
            "pi" => array("nativeLabel" => "Pirate"),
         )
    )
);

return $strata;
?>