re: How much should I invest in international mutual funds in my 401k?

As others have said, at least 10% international would be right for most people.

You could look at VT as well. That’s the total world stock market. I think it’s roughly 35% international currently.

If you are going to target international index funds, I would lean towards emerging markets and avoid Europe. European business is going to die without cheap Russian gas and the EU over regulates everything. I’d also think about whether you want to avoid China. They cutdown their most successful companies when they become too powerful. See Alibaba.