TranslationManager.php

    public function saveValue($key, $value, $locale, $domain = self::DEFAULT_DOMAIN, $scope = Translation::SCOPE_SYSTEM)
    {
        $translationValue = $this->findValue($key, $locale, $domain);
        if (!$this->canUpdateTranslation($scope, $translationValue)) {
            return null;
        }

        if (!$value && $translationValue) {
            $this->getEntityManager(Translation::class)->remove($translationValue);
            return null;
        }

        if (null === $translationValue) {
            $translationValue = $this->createValue($key, $value, $locale, $domain, true);
        }

        $translationValue->setValue($value);
        $translationValue->setScope($scope);

        return $translationValue;
    }