Many of the larger banks in Taiwan offer you the ability to buy foreign funds, but you must first have an account at the bank in the currency of the fund you want to buy. So, for example, if you have an NTD account at your bank and you want to buy a Vanguard index, you’d need a USD account to buy the shares. But these are typically offered as brokerage accounts, meaning you buy and sell shares through the account at your own discretion. If you’re looking to transfer a fixed amount into a mutual fund at fixed intervals, you might need to find something that is more along the lines of a financial advisor or financial planner.
A lot of the large American buy side firms that offer indexes don’t sell their products directly in Taiwan. But, some of them do sell their products through intermediaries or distributors. For example, Capital Group has index funds and sells them in Taiwan through a third party broker based in TW:
If you’re interested in Vanguard funds, check out their website to see if they sell their indexes in TW through a distributor. If they do, contact that distributor and let them know your situation and your financial plans.