Thank you very much for these photos!
I see that this sword had a long and hard life. But he is still a strong and cheerful old gentleman
In my opinion, the blade is quite typical for this part of Indochina. The decor is a stylized image of the constellations. The same or very similar ones were depicted on ancient Vietnamese flags, which, for example, were used in Nam Giao - the ceremony of sacrifice to the Earth and Sky. On Chinese blades, the stylized image of the seven stars of the Big Dipper can often be seen, but this is the first time I see it on a Vietnamese blade. And the style itself is different from the Chinese.
The crack on the handle looks too regular and symmetrical for accidental damage. I can assume that there used to be a decorative insert in this place, for example, a silver stripe.
I have some more thoughts about this sword, but I need to find illustrative material to make my opinion more understandable and justified. This will take a few days or possibly a week.