How do i transfer email folders from one gmail account to another?

1. Enable IMAP in both Gmail accounts.
2. Install an email client software on your computer (e.g Thunderbird or Outlook).
3. Add your Gmail accounts to this client.
4. Copy your email folders from #1 to #2.
5. Done.

Step 4 > Jérôme meant even Drag-n-Drop will work

This is the easiest method which will even maintain sender, receiver, timestamps & attachments