[Backport] Correct a typo in the reference to ISO language codes

[vasilii-b]

Original Pull Request

#18733

Description (*)

Correct a typo in the reference to ISO language codes

Fixed Issues (if relevant)

1. MAGEDOC-2910: Fix typo devdocs#2686: MAGEDOC-2910: Fix typo

Manual testing scenarios (*)

N/A

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @vasilii-b. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me $VERSION instance - deploy vanilla Magento instance

For more details, please, review the Magento Contributor Assistant documentation

[VladimirZaets]

Hi @vasilii-b, thanks for collaboration. Due to Magento Code Contributions processes, we don't accept PRs with code cleanup for 2.2 Magento version.