Java lambdas: Copy nodes from list to a new list

Assuming your Suggestion somewhat possess a public Suggestion copy(); method (like implementing a Copyable<Suggestion> interface), you could do :

List<Suggestion> only_translations = original_list.stream()
    .filter(t -> t.isTranslation)
    .map(t -> t.copy())       // or .map(Suggestion::copy)
    .collect(Collectors.toList()));

EDIT : with the copy constructor :

List<Suggestion> only_translations = original_list.stream()
    .filter(t -> t.isTranslation)
    .map(t -> new Suggestion(t))  // or .map(Suggestion::new)
    .collect(Collectors.toList()));

Since you say you have a copy constructor, just add this before the collect operation to get a list of copied objects:

.map(Suggestion::new)