Hi there,
Sorry for not pointing out the right translations for your first inquiries
You can check on those language files for what those string hold, for example, "joined the group", you can global search and see which string hold them. By the way, those language string are as listed above.
APP_USER_GROUPS_STREAM_HAS_JOIN_GROUP in
../language/en-GB/en-GB.com_easysocial.ini
APP_USER_EASYDISCUSS_STORY in
administrator/language/en-GB/en-GB.plg_app_user_discuss.ini
The link on this page does not work "error 404"
There are some issues on our end and transifex. By the way, i have discuss this with my colleague and it would be best if you can create a new thread and set it as general, then my colleague will help you further on this issues.
Thanks for your understanding