Add multi-language support

Feature request

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Checklist

• This issue is not a duplicate, I've searched the Issue Tracker
• This issue is not a question, I'm aware that I can submit questions via Mastodon, Twitter, Email, Reddit or Matrix
• This issue is a feature request, and not a bug report, content request, or anything other

What are you missing or what could be improved?

GoFOSS should support multiple languages, starting with EN, FR & DE

What is the solution you'd like to see?

[x] Visitors should be able to select their language via a selector in the header bar.

Solution: Material for MkDocs supports internationalization (i18n) and provides translations for template variables and labels. Material for MkDocs also has an experimental feature where a language selector can be added to the header next to the search bar. Alternate languages can be defined via mkdocs.yml.

[x] Once a language is selected, the entire environment should change accordingly.

Solution: everything changes correctly when switching language. This includes page content, sidebar, navigation elements, search bar and so on.

Do you have additional comments?

N/A