Greasy Fork is available in English.
Improved experience for reddit.com
I never used old.reddit so I not so mush understand, but I did it for comments. For posts maybe later. By default the bookmark shows only for an comment which already saved. To show bookmarks always you need to go in settings and uncheck "Hide unsaved bookmark" option.
Great work! And for posts it looks like this on old reddit
please unwrap the 'save' buttons, like in the old reddit!