Greasy Fork is available in English.
If you have a script manager and you want to download some script without installing it, this script will help
< GreasyFork: download script buttonについてのフィードバック
I have the button there. I need to think about that...
What browser do you use and do you have some other scripts/extensions that are changing anything for greasyfork.org?
In order to find the problem I need you to open your browser console and check if you have any errors related to the script in the console.
Also it would be good if you can navigate to the page with the problem, open the console, and send this line into it console.log(document.querySelectorAll('a.install-link'), document.querySelector('div#install-area'), document.querySelectorAll('a.install-help-link')) and send a screenshot with the result here
For some post, the button doesn't appear.
An example: https://greasyfork.org/en/scripts/482577