Yes, you can add non-US companies that you have invested in to your account. Seraf allows you to include companies across the world in your portfolio. Note that you can only save your investments in one currency across your entire account. Therefore, you would need to convert your foreign investments into whichever currency you select as your preferred currency for your account.
To learn more about how to change the currency of your entire account, please see How do I change my default currency?