Document how to merge translations from Crowdin

doc/development/i18n/index.md

@@ -50,3 +50,5 @@ able to proofread and instructions on becoming a proofreader yourself.
 ## Release
 
 Translations are typically included in the next major or minor release.
+
+See [Merging translations from Crowdin](merging_translations.md)

doc/development/i18n/merging_translations.md

+# Merging translations from Crowdin
+
+Crowdin automatically syncs the `gitlab.pot` file presenting newly
+added translations to the community of translators.
+
+At the same time, it creates a merge request to merge all newly added
+& approved translations. Find the [merge reqeust created by
+`gitlab-crowdin-bot`](https://gitlab.com/gitlab-org/gitlab-ee/merge_requests?scope=all&utf8=%E2%9C%93&state=opened&author_username=gitlab-crowdin-bot)
+to see new and merged merge requests. They are created in EE and need
+to be ported to CE manually.
+
+## Validation
+
+By default Crowdin commits translations with `[skip ci]` in the commit
+message. This is done to avoid a bunch of pipelines being run. Before
+merging translations, make sure to trigger a pipeline to validate
+translations, we have static analysis validating things Crowdin
+doesn't do. Create a [new pipeline](https://gitlab.com/gitlab-org/gitlab-ee/pipelines/new) for the
+`master-i18n` branch.
+
+If there are validation errors, the easiest solution is to disapprove
+the offending string in Crowdin, leaving a comment with what is
+required to fix the offense. There is an
+[issue](https://gitlab.com/gitlab-org/gitlab-ce/issues/49208)
+suggesting to automate this process. Disapproving will exclude the
+invalid translation, the merge request will be updated within a few
+minutes.
+
+It might be handy to pause the integration on the Crowdin side for a
+little while so translations don't keep coming. This can be done by
+clicking `Pause sync` on the [Crowdin integration settings
+page](https://translate.gitlab.com/project/gitlab-ee/settings#integration).
+
+When all failures are resolved, the translations need to be double
+checked once more [as discussed in this
+issue](https://gitlab.com/gitlab-org/gitlab-ce/issues/37850).
+
+## Merging translations
+
+When all translations are found good and pipelines pass the
+translations can be merged into the master branch. After that is done,
+create a new merge request cherry-picking the translations from EE to
+CE. When merging the translations, make sure to check the `Remove
+source branch` checkbox, so Crowdin recreates the `master-i18n` from
+master after the new translation was merged.
+
+We are discussing automating this entire process
+[here](https://gitlab.com/gitlab-org/gitlab-ce/issues/39309).
+
+## Recreate the merge request
+
+Crowdin creates a new merge request as soon as the old one is closed
+or merged. But it won't recreate the `master-i18n` branch every
+time. To force Crowdin to recreate the branch, close any [open merge
+request](https://gitlab.com/gitlab-org/gitlab-ee/merge_requests?scope=all&utf8=%E2%9C%93&state=opened&author_username=gitlab-crowdin-bot)
+and delete the
+[`master-18n`](https://gitlab.com/gitlab-org/gitlab-ee/branches/all?utf8=%E2%9C%93&search=master-i18n).
+
+This might be needed when the merge request contains failures that
+have been fixed on master.