I'm pretty sure we saw a Russell's Viper tonight. See http://www.snakesoftaiwan.com/Daboia%20russelli%20siamensis/species_daboia_russelli.htm. When I see patterns similar to the Russell's Viper pattern, I immediately think Habu, but there are a few species that look very similar to Habu, Russell's Viper being one. And, SE Taiwan is apparently one of its main habitats.

I can't be certain, but if I were to choose this snake form a lineup of snakes on snakesoftaiwan.com, that's what it would be.