Copying text out of a comic doesn't work: the words are part of the picture. To read a page you can't read yet, you need a tool that looks at the image itself. Here's how to do it in Chrome with Yakumi, without leaving the page.
Install it from the Chrome Web Store. There's nothing to set up, and your first 20 pages work without an account.
Open the Yakumi menu from the toolbar and choose English, Japanese, Korean, Simplified Chinese or Traditional Chinese.
Hover over a comic image and press Translate, or right-click the image and choose Translate this image. The translation is drawn over the original, inside the speech bubbles. Turn on Auto if you want each image translated as you scroll.

Press Show original any time to see the artwork as it was drawn.
One image is one page. A very tall webtoon image counts 1 page for every 3,000 px of height. A translation that fails doesn't use any pages, and re-opening a page you translated in the last 7 days on the same browser is free.
Machine translation helps you follow a story you can't read yet. When an official translation exists, please support it.