Hi,
You can use the PayPal Pro plugin without SSL. Just turn off SSL on your website. But we can't recommend that as in a lot of countries, it is against the law and it is forbidden by both Visa and Mastercard.
If you want the transaction to be secured without SSL, you need to use the PayPal Standard plugin.
In any case, that is not linked to the fact that you don't see the paypal pro payment method on your checkout. You say that your currency is TWD, however, PayPal Pro service is only offered by PayPal in the USA, Canada and UK. So if you're in Taiwan, it's normal that you don't see the payment method as you can't use it in that country. So really, you should go with PayPal Standard on your website.