Add guide on multilingual datasets

[CaroFG]

Pull Request

Related issue

Fixes #<issue_number>

What does this PR do?

• Adds a guide on handling multilingual datasets

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• Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
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Thank you so much for contributing to Meilisearch!

[guimachiavelli]

Since the "Guides" section atm is very focussed on integrating Meilisearch with third-party libs/tools (e.g. use meilisearch with mistral, deploy on AWS, etc) I'm thinking that adding it to /learn/indexing might actually make more sense. What do you think?

Other than that, I made a couple of suggestions to reduce the size of the article a bit.