"How do I report these shares I sold in my 2018 taxes?"
You use the "Stocks, Mutual Funds, Bonds, Other" interview and tell TurboTax you did not receive a 1099-B.
"Do I have to indicate that these were foreign shares anywhere?"
For purposes of the sale? NO.
"Do I just find the price per share on the day I vested in US dollars and
my cost basis is only the shares I received, and not the ones withheld?"
Your per share cost basis is the same as the per share "fair market value" used by the employer to report the compensation created by the vesting in 2015.
Compensation on W-2 = GROSS number of shares vesting x per share "fair market value"
If you can't figure this out then, if the stock is publicly traded, use the closing price on the day of vesting as an estimate of your per share basis.
You multiply this "per share" number times the number of shares sold as your cost.
There's absolutely NO NEED to use the RSU Guide me step by step interview here. Just use the default "stock" interview, entering the correct numbers.
Tom Young