Greasy Fork is available in English.
Change YouTube leftbar's subscription links to channel/user video page. This script can optionally also move updated links to top of the list (if there's enough space), optionally uncollapse all updated links which may extend the non collapsible links, and optionally display the number of updated & total links following the "SUBSCRIPTION" section label. All features can be enabled/disabled from the script code. For new YouTube layout only.
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EDIT: OK, just noticed that if I click on the channels HOME tab, it marks it properly - I have it set to redirect to the VIDEO tab in the script, which I'd like to keep on if at all possible.
Whatever the issue was seems to have sorted itself out on YouTube's end, so please disregard.
Subscription link count update seems borked again, isn't marking viewed/clicked on channels - at least on my end of things.