累 更口语化， 疲倦书面化

累，表示做了事情，跟体力有关！ 疲倦，表示时间困惑，跟精神有关！

累 is often used in spoken language while 疲倦 is much more fomal than 累. In China, people always say 累死了, which means i am so tired.

“累”is oral Chinese, and“ 疲倦” is a formal usage. When you talk to a person, you'd better say somebody”累“ or ”累了/很累“.

累比较生活语化