docs: refactor sidebar label translations examples to use tags with regional subtags

[HiDeoo]

What kind of changes does this PR include?

• Changes or translations of Starlight docs site content

Description

This pull request is an attempt to improve the documentation regarding the translation of sidebar labels following this issue on Discord. The scenario is the following:

• A user wants to translate some sidebar labels to some language, in this case, Brazilian Portuguese.
• After checking the sidebar guide and the Configuration Reference, they use the following configuration:

{
  label: 'Getting Started',
  translations: { 'pt-br': 'Introdução' },
  link: '/getting-started',
}

Altho, this configuration does not translate the sidebar link label due to the fact that the key of the translations object should use a BCP-47 tag as key, which would be pt-BR in this case while the user thought it should be pt-br and match their file system structure.

To improve this, this PR proposes the following changes:

• Sidebar guide
  • Explicitely mention that a BCP-47 language tag should be used as key with some examples
  • Update the example to translate to Brazilian Portuguese instead of Spanish
• Configuration Reference
  • Update the example to translate to Brazilian Portuguese instead of French

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Latest commit: 3a64482

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[delucis]

This is great — thank you @HiDeoo!

Let’s hold off before merging this — I’d love to get a few outstanding translation PRs in before.

[delucis]

Lovely! Merge whenever you like @HiDeoo 🌟