OK, please let me answer yourquestion. 1."XX的" in Chinese is equal to a adjective in English. so when you translate an adjective into Chinese, maybe you should remember to take the "的". for example, in your sentence, "this new bag is beautiful", here, "new" and "beautiful" are both adjective, so it should be translated as "新的" or "漂亮的". 2.sometimes, when you can use Chinese flexibly, you will find some"的" can be omitted( and in Chinese, it means"省略"). And both"它是一件新衣服" and "它是一件新的衣服" are right.

Hi, I see the point. Thank you very much.

1.Hi，When you want to emphasis it is new, this "的",because the structure：是。。。。的； Eg：这个新包是我的。 2.In oral we omit "的“，when "的”between Adj.and Noun.新（的）包，新（的）手机。 so if you want to say :new things, omit that "的"。Chinese mostly will say：这个新包 .instead of 这个新的包。