Do you know any Vietnamese novel translated in English ?

I would suggest you read the epic poem The Tale of Kiều written by Nguyễn Du.  Consider this from the forward of a translation by Huỳnh Sanh Thông published by Yale University Press.

“Western readers who are curious about Vietnam and the Vietnamese may well gain more real wisdom from cultivating a discriminating appreciation of this one poem than they will from reading the entire library of scholarly and journalistic writings upon modern Vietnam which has accumulated in the West in the past two decades.”

English translations should be readily available in HCMC bookstores.  The most common is a translation by William Counsell.    There was also a French translation by a Nguyễn Khắc Viện who was a high ranking revolutionary official.  Apparently he fell out of Party favor late in life so his work may not be readily available within Vietnam.

You can find "Give me a ticket to childhood"- Nguyễn Nhật Ánh (translated by William Naythons)

Hi, thx for your suggestions !

I just started "Last night I dreamed of peace" from Đặng Thùy Trâm. I bought it to a street seller, and I must say it's my first encounter with a "false copy" (or I don't know how you name that in English), with plenty of misspelling every pages. Still readable though.

try " the beauty of humanity " a story based in truth of a young boy and his family old  and young survival during the American war and to present time in Hanoi. Very insiteful and at time, moving, if you are in Saigon try "garden street in town, walk down toward the ferry terminal on the left are lots of book stores, if you go there during TET / new year the book sellers have huge sales on the Hai Ba Trung street

Ms. Judith Henchy, of the University of Washington's library department, compiled a list:

Contemporary Vietnamese Fiction in Translation

The first place I'd start a search would be at over at Project Gutenberg

Happy hunting!