twigphp/Twig · error · InvalidArgumentException

Locale " " is not supported.

Error message

Locale "%s" is not supported.

What it means

StringExtension::getInflector() maps a locale to a doctrine/inflector implementation (English, Spanish, French, ...). When the locale has no case in its switch, it throws an InvalidArgumentException. The plural/singular filters accept a locale argument, and only a fixed set of languages is supported.

Solutions

1. Use a supported locale: 'en', 'es', 'fr' (check the extension's switch for the exact set).
2. Normalize the locale to its primary subtag and default to 'en' when unsupported, e.g. explode('_', $locale)[0] with a fallback.
3. For other languages, subclass StringExtension and override getInflector() to plug in your own doctrine/inflector rules.

Example fix

// before
{{ word|plural(app.request.locale) }}  {# locale = "de_DE" #}
// after
{% set loc = app.request.locale|split('_')[0] %}
{{ word|plural(loc in ['en','es','fr'] ? loc : 'en') }}

$supported = ['en', 'es', 'fr'];
$loc = explode('_', $locale)[0];
if (!in_array($loc, $supported, true)) {
    $loc = 'en'; // or skip the filter
}

try {
    $out = $twig->render($tpl, ['word' => $word, 'locale' => $loc]);
} catch (\InvalidArgumentException $e) {
    // unsupported locale; fall back to default inflection
}

When it happens

Trigger: Calling the plural or singular Twig filters with an unsupported locale argument, e.g. {{ 'cats'|plural('de') }} or {{ 'chats'|singular('it') }}, where 'de'/'it' are not handled by getInflector's switch.

Common situations: Passing the app's locale straight into the filter (apps commonly run de_DE, it_IT, pt_BR); locale strings like 'pt_BR' or with charset suffix 'fr_FR.UTF-8' that don't match bare case labels like 'fr'; assuming all ICU locales are supported.

Related errors

• A block chain requires at least one template.
• The "format_list" filter requires the "IntlListFormatter"…
• The date format " " does not exist, known formats are: " ".
• The time format " " does not exist, known formats are: " ".
• The style " " does not exist, known styles are: " ".

AI-assisted analysis of twigphp/Twig@a414c3a491 (2026-09-13). Data as JSON: /api/errors/ea4b163a36e5a8d0. Report an issue: GitHub.

Appendix: source

Thrown at extra/string-extra/StringExtension.php:96

        return $this->getInflector($locale)->singularize($value)[0];
    }

    private function getInflector(string $locale): InflectorInterface
    {
        switch ($locale) {
            case 'en':
                return $this->englishInflector ?? $this->englishInflector = new EnglishInflector();
            case 'es':
                if (!class_exists(SpanishInflector::class)) {
                    throw new RuntimeError('SpanishInflector is not available.');
                }

                return $this->spanishInflector ?? $this->spanishInflector = new SpanishInflector();
            case 'fr':
                return $this->frenchInflector ?? $this->frenchInflector = new FrenchInflector();
            default:
                throw new \InvalidArgumentException(\sprintf('Locale "%s" is not supported.', $locale));
        }
    }
}

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