Translation:Your room is too dirty!
Your room is so messy! I know messy is 'luan' but in English dirty and messy are sometimes interchangeable (like in this sentence).
But it is not so interchangeable in Chinese. Too emphasize “messy” we can say 乱, or 脏乱 if you want to include the word 脏.
Why is 了 in this sentence. Usually when using 了 it describes a change in the situation. The person talking is just pointing something out not necessarily doing something to change the situation, maybe something like "your room will be too dirty" calls for the 了.
It is easier if you just think it is a set pattern: 太+adj.+了
If you want to be logical and see how a change can be indicated by 了, this sentence is like saying “your room has become too dirty”.