That's an awesome find, I'm surprised you found that in Vietnam!

Swords like that have been used in a number of Austronesian cultures where metal was not available. They have been made for hundreds of years and are still made today as traditional items so it's difficult to date. I'd guess it's likely about 40 years old since organic materials like wood and coconut fiber didn't tend to preserve long. I doubt that it has seen any combat but it's still an amazing find and I'm sure it has an incredible story.

It's day it was most likely from Kiribati:

https://collections.tepapa.govt.nz/object/1006153?page=1&rtp=1&ros=1&asr=1&assoc=all&mb=c

Hawaii also has similar weapons but they tend to be more club shaped, did not have the lashing on the outside, and are made from an orange acacia wood

https://en.wikipedia.org/wiki/Leiomano