Merge branch 'review-youtrack-docs' into 'master'

YouTrack docs review

Closes #58225

See merge request gitlab-org/gitlab-ce!26454

doc/integration/external-issue-tracker.md

 # External issue tracker
 
-GitLab has a great issue tracker but you can also use an external one such as
-Jira, Redmine, YouTrack, or Bugzilla. Issue trackers are configurable per GitLab project
-and allow you to do the following:
+GitLab has a great [issue tracker](../user/project/issues/index.md) but you can also use an external one
+such as Jira, Redmine, YouTrack, or Bugzilla. External issue trackers are configurable per GitLab project.
 
-- you can reference these external issues inside GitLab interface
-  (merge requests, commits, comments) and they will be automatically converted
-  into links
+Once configured, you can reference external issues using the format CODE-123, where CODE is a unique code
+for the tracker, and 123 is the issue number in the tracker. These references in GitLab 
+merge requests, commits, or comments are automatically converted to links to the issues.
 
-You can have enabled both external and internal GitLab issue trackers in parallel. The **Issues** link always opens the internal issue tracker and in case the internal issue tracker is disabled the link is not visible in the menu.
+You can keep GitLab's issue tracker enabled in parallel or disable it. When enabled, the **Issues** link in the
+GitLab menu always opens the internal issue tracker. When disabled, the link is not visible in the menu.
 
 ## Configuration
 

doc/user/project/integrations/youtrack.md

 # YouTrack Service
 
-JetBrains YouTrack is a web-based issue tracking and project management platform.
-Please refer official [documentation](https://www.jetbrains.com/help/youtrack/standalone/YouTrack-Documentation.html) for details about YouTrack itself.
+JetBrains [YouTrack](https://www.jetbrains.com/help/youtrack/standalone/YouTrack-Documentation.html) is a web-based issue tracking and project management platform.
 
+You can configure YouTrack as an [External Issue Tracker](../../../integration/external-issue-tracker.md) in GitLab.
 
-1. To enable the YouTrack integration in a project, navigate to the
-[Integrations page](project_services.md#accessing-the-project-services), click
-the **YouTrack** service, and fill in the required details on the page as described
+## Enable the YouTrack integration in a project
+
+Navigate to the [Integrations page](project_services.md#accessing-the-project-services), click
+the **YouTrack** service, and enter the required details on the page as described
 in the table below.
 
     | Field | Description |
@@ -15,17 +16,19 @@ in the table below.
     | `project_url`   | The URL to the project in YouTrack which is being linked to this GitLab project |
     | `issues_url`    | The URL to the issue in YouTrack project that is linked to this GitLab project. Note that the `issues_url` requires `:id` in the URL. This ID is used by GitLab as a placeholder to replace the issue number. |
 
-    Once you have configured and enabled YouTrack you'll see the YouTrack link on the GitLab project pages that takes you to the appropriate YouTrack project.
+Once you have configured and enabled YouTrack you'll see the YouTrack link on the GitLab project pages that takes you to the appropriate YouTrack project.
+
+## Disable the internal issue tracker in a project
 
-1. To disable the internal issue tracking system in a project, navigate to the General page, expand [Permissions](../settings/index.md#sharing-and-permissions), and slide the Issues switch invalid.
+Navigate to the General page, expand [Permissions](../settings/index.md#sharing-and-permissions), and switch the Issues toggle to disabled.
 
-    ![Issue configuration](img/issue_configuration.png)
+![Issue configuration](img/issue_configuration.png)
 
-## Referencing issues in YouTrack
+## Referencing YouTrack issues in GitLab
 
-Issues in YouTrack can be referenced as `<PROJECT>-<ID>` where `<PROJECT>`
-starts with a capital letter which is then followed by capital or lower case
-letters, numbers or underscores, and `<ID>` is a number (example `Api_32-143`).
+Issues in YouTrack can be referenced as `<PROJECT>-<ID>`. `<PROJECT>`
+must start with a capital letter and can then be followed by capital or lower case
+letters, numbers or underscores. `<ID>` is a number. An example reference is `YT-101` or `Api_32-143`.
 
-`<PROJECT>` part is included into issue_id and links can point any YouTrack
-project (`issues_url` + issue_id)
+References to <PROJECT>-<ID> in merge requests, commits, or comments are automatically linked to the YouTrack issue URL.
+For more information, see the [External Issue Tracker](../../../integration/external-issue-tracker.md) documentation.