Tax on US Retirement Accounts (401K/IRA) Roth and Traditional. US/Spain

I am a 30 year old, Cuban/American citizen, planning to move to Spain in the short term and become a Spanish citizen. I’ve been contributing to a Roth 401K and Roth IRA. I am looking for some indication of how those accounts are taxed at retirement age; my searches have given me a lot of mixed responses.