phpbb_ynh/sources/phpBB/language/en/email/admin_activate.txt

Subject: Activate user account

Hello,

The account owned by "{USERNAME}" has been deactivated or newly created, you should check the details of this user (if required) and handle it appropriately.

Use this link to view the user's profile:
{U_USER_DETAILS}

Use this link to activate the account:
{U_ACTIVATE}

{EMAIL_SIG}