public function getPluralForms(Locale $locale)
    {
        if (!isset($this->rulesetsIndices[$locale->getLanguage()])) {
            return [self::RULE_OTHER];
        }

        $ruleset = $this->rulesets[$locale->getLanguage()][$this->rulesetsIndices[$locale->getLanguage()]] ?? null;

        if ($ruleset === null) {
            return [self::RULE_OTHER];
        }

        return array_merge(array_keys($ruleset), [self::RULE_OTHER]);
    }