Traduko - Angla-Čina - I am a lost smile...

It can not be better than that, is exactly what the words are saying. Hope it is ok.
In Romanian, we let the pronoun out, it can be understood from the context what should it be there. Can create confusion for people that are not natives, especially because "sunt" means both "are" and "am". For me, sounds much better if it is used "I am" instead of "they are". Because then it should be "Ei sunt nişte zâmbete pierdute...". Slightly different.
The expression is poetic.

Have modified it to sound romantic in Chinese. Literally translated back to English is "I am a smile lost in the wind."