ContentTranslationController::add should give a helpful message once a translation already exists.

Drupal 8.0.6 was released on April 6 and is the final bugfix release for the Drupal 8.0.x series. Drupal 8.0.x will not receive any further development aside from security fixes. Drupal 8.1.0-rc1 is now available and sites should prepare to update to 8.1.0.

Bug reports should be targeted against the 8.1.x-dev branch from now on, and new development or disruptive changes should be targeted against the 8.2.x-dev branch. For more information see the Drupal 8 minor version schedule and the Allowed changes during the Drupal 8 release cycle.

Drupal 8.1.9 was released on September 7 and is the final bugfix release for the Drupal 8.1.x series. Drupal 8.1.x will not receive any further development aside from security fixes. Drupal 8.2.0-rc1 is now available and sites should prepare to upgrade to 8.2.0.

Bug reports should be targeted against the 8.2.x-dev branch from now on, and new development or disruptive changes should be targeted against the 8.3.x-dev branch. For more information see the Drupal 8 minor version schedule and the Allowed changes during the Drupal 8 release cycle.

Drupal 8.2.6 was released on February 1, 2017 and is the final full bugfix release for the Drupal 8.2.x series. Drupal 8.2.x will not receive any further development aside from critical and security fixes. Sites should prepare to update to 8.3.0 on April 5, 2017. (Drupal 8.3.0-alpha1 is available for testing.)

Bug reports should be targeted against the 8.3.x-dev branch from now on, and new development or disruptive changes should be targeted against the 8.4.x-dev branch. For more information see the Drupal 8 minor version schedule and the Allowed changes during the Drupal 8 release cycle.

Drupal 8.3.6 was released on August 2, 2017 and is the final full bugfix release for the Drupal 8.3.x series. Drupal 8.3.x will not receive any further development aside from critical and security fixes. Sites should prepare to update to 8.4.0 on October 4, 2017. (Drupal 8.4.0-alpha1 is available for testing.)

Bug reports should be targeted against the 8.4.x-dev branch from now on, and new development or disruptive changes should be targeted against the 8.5.x-dev branch. For more information see the Drupal 8 minor version schedule and the Allowed changes during the Drupal 8 release cycle.

Drupal 8.4.4 was released on January 3, 2018 and is the final full bugfix release for the Drupal 8.4.x series. Drupal 8.4.x will not receive any further development aside from critical and security fixes. Sites should prepare to update to 8.5.0 on March 7, 2018. (Drupal 8.5.0-alpha1 is available for testing.)

Bug reports should be targeted against the 8.5.x-dev branch from now on, and new development or disruptive changes should be targeted against the 8.6.x-dev branch. For more information see the Drupal 8 minor version schedule and the Allowed changes during the Drupal 8 release cycle.

Drupal 8.5.6 was released on August 1, 2018 and is the final bugfix release for the Drupal 8.5.x series. Drupal 8.5.x will not receive any further development aside from security fixes. Sites should prepare to update to 8.6.0 on September 5, 2018. (Drupal 8.6.0-rc1 is available for testing.)

Bug reports should be targeted against the 8.6.x-dev branch from now on, and new development or disruptive changes should be targeted against the 8.7.x-dev branch. For more information see the Drupal 8 minor version schedule and the Allowed changes during the Drupal 8 release cycle.

Drupal 8.6.x will not receive any further development aside from security fixes. Bug reports should be targeted against the 8.8.x-dev branch from now on, and new development or disruptive changes should be targeted against the 8.9.x-dev branch. For more information see the Drupal 8 and 9 minor version schedule and the Allowed changes during the Drupal 8 and 9 release cycles.

Drupal 8.8.7 was released on June 3, 2020 and is the final full bugfix release for the Drupal 8.8.x series. Drupal 8.8.x will not receive any further development aside from security fixes. Sites should prepare to update to Drupal 8.9.0 or Drupal 9.0.0 for ongoing support.

Bug reports should be targeted against the 8.9.x-dev branch from now on, and new development or disruptive changes should be targeted against the 9.1.x-dev branch. For more information see the Drupal 8 and 9 minor version schedule and the Allowed changes during the Drupal 8 and 9 release cycles.

Drupal 8 is end-of-life as of November 17, 2021. There will not be further changes made to Drupal 8. Bugfixes are now made to the 9.3.x and higher branches only. For more information see the Drupal core minor version schedule and the Allowed changes during the Drupal core release cycle.

Drupal 9.3.15 was released on June 1st, 2022 and is the final full bugfix release for the Drupal 9.3.x series. Drupal 9.3.x will not receive any further development aside from security fixes. Drupal 9 bug reports should be targeted for the 9.4.x-dev branch from now on, and new development or disruptive changes should be targeted for the 9.5.x-dev branch. For more information see the Drupal core minor version schedule and the Allowed changes during the Drupal core release cycle.