Translate all static pages to Spanish

[maelle]

For clarification, babeldown would do the first translation! For each translation, I will also need to manually edit HTML templates to add i18n variables.

Outside of the blog, we don't have that much content so it's not a too big endeavor.

Not to translate

• 404
• events? What to do about "events" #510
• use cases? What to do about use cases #511
• news page? What to do about the newsletter page? #515

To translate

• about.md (actually not Markdown content)
• champions/_index.md
• citations/_index.md
• commcalls/_index.md
• community/_index.md
• contact/_index.md
• donate/_index.md
• help-wanted/_index.md
• how-to-cite-ropensci.md
• multilingual-publishing/_index.md
• packages/_index.md + other Markdown files.
• papers/_index.md
• resources/_index.md
• r-universe/_index.md
• software-review/_index.md
• stat-software-review/_index.md

[yabellini]

Yes, I will do the review. :-)