So you want to take the top 5 news items for the current language, and then filter out any where subscriber 5 isn't subscribed?
IEnumerable<NewsItem> result = newsItemCollection._newsItems
.Where(n => n.Language == language)
.Take(5)
.Where(n => n.Subscribers.Any(s => s.Id == 5))
;
If you want to take the top 5 items for the subscriber, move the
Take
call after the second
Where
call.