a friend in need is a friend indeed. 
患难见真情 

a hedge between keeps friendship green. 
君子之交淡如水。 

without a friend,the world is a wilderness. 
没有朋友，世界成了荒野。 

friendship is like wine—the older the better. 
友谊像美酒，越陈越醇厚。 

a friend is a second self. 
朋友是第二个自我。 

a friend is best found in adversity. 
患难识真友。