symfony/translation · error · InvalidArgumentException

Invalid " " locale.

Error message

Invalid "%s" locale.

What it means

Static guard in LocaleFallbackProvider (Translation provider layer) that rejects locale strings containing characters outside [a-zA-Z0-9@_.-]. It is called when constructing the provider and when computing fallback locales, because an invalid locale would silently produce broken catalogue lookups.

Solutions

1. Fix the locale string so it matches /^[a-z0-9@_\.\-]*$/i (e.g. 'en', 'en_US', 'fr@posix').
2. If passing multiple locales, pass an array or split on a valid separator instead of embedding them in one string.
3. Trim whitespace and strip query fragments from user-supplied locales before use.
4. Call LocaleFallbackProvider::validateLocale($locale) yourself in config bootstrapping to fail early with a clearer message.

Example fix

// before
new LocaleFallbackProvider($loader, 'en_US de_DE');

// after
new LocaleFallbackProvider($loader, 'en_US');

if (!preg_match('/^[a-z0-9@_\.\-]*$/i', $locale)) {
    throw new \InvalidArgumentException("Locale '$locale' contains invalid characters");
}

function isValidLocale(string $locale): bool { return (bool) preg_match('/^[a-z0-9@_\.\-]*$/i', $locale); }

try {
    $provider = new LocaleFallbackProvider($loader, $locale);
} catch (\InvalidArgumentException $e) {
    // sanitize/fix $locale before retrying
}

When it happens

Trigger: Passing a locale containing spaces, slashes, commas, uppercase-extended symbols or other invalid characters to new LocaleFallbackProvider(...), to fallback locale configuration (computeFallbackLocales), or via helpers like assertValidLocale.

Common situations: Environment variables or config containing 'en_US;de_DE' lists with semicolons, URLs accidentally used as locales, locales with spaces ('en US'), or user-supplied locale input injected into fallback configuration.

Understand the failure class

Background: "invalid id" errors: invalid identifier format — why libraries reject IDs before lookup, and how to fix them — this error's family across 37 libraries.

Related errors

• There is no dumper associated with format
• $batch argument must be one of

AI-assisted analysis of symfony/translation@ae9e8a51bc (2026-09-15). Data as JSON: /api/errors/2d43dceae823e13e. Report an issue: GitHub.

Appendix: source

Thrown at LocaleFallbackProvider.php:92

            if ($fallback === $originLocale) {
                continue;
            }

            $locales[$fallback] = $fallback;
        }

        return array_keys($locales);
    }

    /**
     * Asserts that the locale is valid, throws an Exception if not.
     *
     * @throws InvalidArgumentException If the locale contains invalid characters
     */
    public static function validateLocale(string $locale): void
    {
        if (!preg_match('/^[a-z0-9@_\.\-]*$/i', $locale)) {
            throw new InvalidArgumentException(\sprintf('Invalid "%s" locale.', $locale));
        }
    }
}

View on GitHub (pinned to ae9e8a51bc)