[BUG] Docker Image's `I18N_LOCALE` environment variable does not seem to work

[linghengqian]

Describe the bug

A clear and concise description of what the bug is.

• Docker Image's I18N_LOCALE environment variable does not seem to work. But I18N_LOCALE is actually documented as follows. See https://github.com/opensearch-project/OpenSearch-Dashboards/blob/2.16.0/src/dev/build/tasks/os_packages/docker_generator/resources/bin/opensearch-dashboards-docker#L54 .
• PRs like #7686 show that i18n is actually ready, if I understand correctly? But I can't find any description of i18n in the configuration section of the documentation.

To Reproduce Steps to reproduce the behavior:

1. Create the following docker-compose.yml file. Then docker compose up -d.

   services:
   opensearch-node1:
   image: opensearchproject/opensearch:2.16.0
   expose:
     - 9200
     - 9600
   environment:
     discovery.type: single-node
     OPENSEARCH_INITIAL_ADMIN_PASSWORD: opensearchNode1Test
   restart: always
   volumes:
     - opensearch-data1:/usr/share/opensearch/data
   opensearch-dashboards:
   image: opensearchproject/opensearch-dashboards:2.16.0
   environment:
     OPENSEARCH_HOSTS: '["https://opensearch-node1:9200"]'
     I18N_LOCALE: "zh-CN"
   restart: always
   ports:
     - "5601:5601"
   volumes:
   opensearch-data1:

2. Visit localhost:5601 and log in using the admin and opensearchNode1Test user passwords.

   • 

3. At this time, the Web UI is still in English, not the Chinese zh-CN set by I18N_LOCALE.

   • 

Expected behavior A clear and concise description of what you expected to happen.

• The I18N_LOCALE environment variable of the Docker Image works.

OpenSearch Version Please list the version of OpenSearch being used.

• 2.16.0

Dashboards Version Please list the version of OpenSearch Dashboards being used.

• 2.16.0

Plugins Please list all plugins currently enabled.

• Only built-ins.

Screenshots

If applicable, add screenshots to help explain your problem.

Host/Environment (please complete the following information):

• OS: [e.g. iOS] Ubuntu 22.04.4 WSL
• Browser and version [e.g. 22] Microsoft Edge 128.0.2739.63

Additional context

• Null.

Add any other context about the problem here.

[Qithird]

遇到同样问题，检测了对多遍以为配置没生效，结果容器中配置已生效只是没有应用到语言包

[linghengqian]

遇到同样问题，检测了对多遍以为配置没生效，结果容器中配置已生效只是没有应用到语言包

• @ananzh I saw #7686 introduced the ability to dynamically change the i18n language via URL. But is there a corresponding documentation PR? And what else needs to be done on the dashboards side to make the i18n configuration permanent?