Hm, how did you generate that string? It should be something like this,

[gist]
APP_PAGE_STORY_USER_COMMENTED_ON_LINK_PAGE="%1$s commented on the link shared in {b}%2$s{/b}"
[/gist]

I don't understand. I have this line in the file, and on the website isn't displayed

In the file - APP_PAGE_STORY_USER_COMMENTED_ON_LINK_PAGE="%1$s commented on the link shared in {b}%2$s{/b}"
Site - APP_PAGE_STORY_USER_COMMENTED_ON_LINKPAGE

Hi Albert,
It seems there is a typo in the following file:
JoomlaFolder/media/com_easysocial/apps/page/story/hooks/notification.comments.php

Can you download the attached fixed file below and check on the issue again to see if it's resolved? Thanks.
This fix will also be included in the next EasySocial release.