It’s worth noting too that Indonesian has a whole bunch of compound expressions with “mudah” used like this. Just a few examples: mudah lupa - easily forgotten; mudah dibawa - portable (easy to carry); mudah didekati - approachable (easily got near to); mudah disukai - likable (easy to like); mudah rusak - breakable (easily broken).
Hahaha....well, it's very intuitive actually :)
Try to look at it like this :
Gaun ini kotor. = This dress is dirty
Gaun ini mudah kotor. = This dress is easily dirty
Both Indonesian sentences don't have verbs.
However, in the English sentence a verb has to be used.
In this case the verb "to be" is used, you can also use "to become".
Gaun ini mudah kotor. ==>
This dress is easily dirty.
This dress is easy to get dirty.
This dress becomes dirty easily.
This dress easily becomes dirty.
All the above translations are accepted.
If you want to use a verb (to become = menjadi) in the Indonesian sentence, then it could be something like this :
"Gaun ini mudah menjadi kotor."
(more or less a literal translation of the last Englsh sentence).