I assume you are filling out a US tax form 1040 and have both US and South Korean income. The IRS does not need to see your South Korean tax return, but you must declare the foreign income on the Form 1040. To prevent or mitigate double taxation, you may be eligible to claim either the Foreign Earned Income Tax Exclusion (by completing Form 2555) or the Foreign Tax Credit (by completing Form 1116). You may also be able to take an increased deduction as an alternative to completing Form 1116 but this is not beneficial for most people.
The effect of the Foreign Earned Income Exclusion is to ignore all your foreign income if it falls below a certain limit. The effect of the Foreign Tax Credit is to reduce your US tax bill on your worldwide income by the amount of the overseas taxes paid.
Turbotax can handle the Foreign Earned Income Exclusion and the Foreign Tax Credit or Deduction. So you should be able to file electronically without the need to mail anything in and therefore no need to translate anything.
