♻️ refactor: improve stylised feed translations & consolidate XSL/CSS loading

[welpo]

This PR builds on the work of PR #96, further enhancing the internationalization handling and consolidating the XSL and CSS loading for the Atom feeds.

Key changes include:

1. Unification of Translations into config.toml: All translations have been moved into config.toml and are loaded into a custom subspace within atom.xml. This change greatly simplifies the handling and extension of multilingual support in the feeds.

2. Consolidation of XSL Logic: Instead of having separate XSL files for each language, this consolidates all XSL logic into a single file. This unified XSL file dynamically adapts the language, offering a more streamlined and maintainable approach.

3. Universal CSS Loading: Fixes the loading of main.css, ensuring it properly loads regardless of the current language or domain setup. This guarantees a consistent styling across all language versions of the feeds.

This refactoring and consolidation not only simplify the codebase, making it more maintainable, but also enhance the feed's multi-language support. Future language additions should be much more straightforward, requiring only additions to the config.toml file, instead of creating extra xsl files.