Is thập niên and thập kỷ interchangeable?
I would like to know this also.
Yes it's the same
thập niên 十年 (Mandarin shínián, Cantonese sap6 nin4)
thập means a cross :-)
i think '10 years' can be an alternative answer (what is the synonym of a decade?)
Not really since when you want to specifically say 10 years in Vietnamese you'd say "mười năm". A decade refers to the year bracket (90s, 2000s, 2010s)
Although a decade consists of ten years these terms are not always interchangable.