Please note that this is not an official extension from DeepL. The official one is here
If you want to see the untranslated version of the page, click the extension icon again. This feature supports multiple tabs.
Clicking again will show the translated version but not the page cause the translator has some limitations. If you still want to retranslate the page, for example because the content has changed, refresh the page and click the extension icon.
First, download the ZIP archive and unzip it to a convenient place.
Then follow "chrome://extensions/", enable developer mode, click on Load unpacked and select the unpacked archive you installed. For your convenience, pin the extension icon.
Almost done. Now go to this link and select the language you want to translate to, as shown at the beginning. The extension uses a web version of the translator DeepL to translate, so it requires an active tab with the translator itself, if necessary the extension itself will open a tab, and when the translation is finished you can close it. Don't worry, you won't need to select the language again. The translator remembers your choice.