Hi Le Xuan Thinh
In 2005 I did some work on difficulties in pronunciation encountered by Vietnamese speakers of English in Australia as part of my TESOL qualification. I have listed some of the references I found very useful at the time but these are dated now and you can find more recent information here
BINH, D. & GAGE, W. (1975) (1975). Vietnamese-English phrasebook with useful words list. Virginia: Centre for Applied Linguistics
HONEY, P. (1987). �Vietnamese Speakers�. In SWAN, M. & SMITH, B. (eds.) Learner English: A teacher�s guide to interference and other problems. Cambridge University Press.
JONES, F. (1999). The difficulties Vietnamese learners face when learning English pronunciation. Proceedings of 1999 M.Teach Post Internship Conference, University of Sydney, 27-29 September 1999. http://alex.edfac.usyd.edu.au/archived%20conferences/conference99/student_papers/Jones.htm
NGUYEN, T. & INGRAM, J. (2004). A corpus-based analysis of transfer effects and connected speech processes in Vietnamese English. Proceedings of the 10th Australian International Conference on Speech Science and Technology, Macquarie University, Sydney, December 8-10 2004.
Good luck!
Cheers
Jayho
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