While unofficial sources exist, the safest and highest-quality way to watch is through official streaming platforms that allow you to add Vietnamese subtitles:
Phim Inception Kẻ Cắp Giấc Mơ (Thuyết Minh) - BiliBili Inception Full Hd Vietsub
: Frequently carries the title in various regions. Check your local Netflix library to see if it's currently available in Vietnam. While unofficial sources exist