/// <summary>
        /// Gets a <see cref="IEnumerable{CultureInfo}"/> containing <see cref="CultureInfo"/> instances from provided <code>requiredTranslations</code>
        /// which translations are not found in the provided <see cref="MarketDescriptionCacheItem"/>
        /// </summary>
        /// <param name="item">The <see cref="MarketDescriptionCacheItem"/> instance, or a null reference</param>
        /// <param name="requiredTranslations">The <see cref="IEnumerable{CultureInfo}"/> specifying the required languages</param>
        /// <returns>A <see cref="IEnumerable{CultureInfo}"/> containing missing translations or a null reference if none of the translations are missing</returns>
        private IEnumerable <CultureInfo> GetMissingTranslations(MarketDescriptionCacheItem item, IEnumerable <CultureInfo> requiredTranslations)
        {
            var requiredTranslationsList = requiredTranslations?.ToList();

            Guard.Argument(requiredTranslationsList, nameof(requiredTranslationsList)).NotNull().NotEmpty();

            if (item == null)
            {
                //return requiredTranslations;
                //we get only those which was not yet fetched
                if (requiredTranslationsList != null)
                {
                    return(requiredTranslationsList.Where(c => !_fetchedLanguages.Contains(c)));
                }
            }

            if (requiredTranslationsList != null)
            {
                var missingCultures = requiredTranslationsList.Where(c => !item.HasTranslationsFor(c)).ToList();

                return(missingCultures.Any()
                    ? missingCultures
                    : null);
            }

            return(null);
        }
        /// <summary>
        /// Gets a <see cref="IEnumerable{CultureInfo}"/> containing <see cref="CultureInfo"/> instances from provided <code>requiredTranslations</code>
        /// which translations are not found in the provided <see cref="MarketDescriptionCacheItem"/>
        /// </summary>
        /// <param name="item">The <see cref="MarketDescriptionCacheItem"/> instance, or a null reference</param>
        /// <param name="requiredTranslations">The <see cref="IEnumerable{CultureInfo}"/> specifying the required languages</param>
        /// <returns>A <see cref="IEnumerable{CultureInfo}"/> containing missing translations or a null reference if none of the translations are missing</returns>
        private IEnumerable <CultureInfo> GetMissingTranslations(MarketDescriptionCacheItem item, IEnumerable <CultureInfo> requiredTranslations)
        {
            Guard.Argument(requiredTranslations, nameof(requiredTranslations)).NotNull();
            if (!requiredTranslations.Any())
            {
                throw new ArgumentOutOfRangeException(nameof(requiredTranslations));
            }

            if (item == null)
            {
                //return requiredTranslations;
                //we get only those which was not yet fetched
                return(requiredTranslations.Where(c => !_fetchedLanguages.Contains(c)));
            }

            var missingCultures = requiredTranslations.Where(c => !item.HasTranslationsFor(c)).ToList();

            return(missingCultures.Any()
                ? missingCultures
                : null);
        }