docs(translation): set a translation release policy

The site is currently being translated into multiple languages, but the work in most languages is just starting.

The language with the most strings translated is at 30% completion.

We should discuss and decide on a policy for when to release a language to the site.

Releasing languages with just a few strings translated will confuse users because most text will appear in English.

Waiting until a translation reaches 100% to release might take a long time.

I would suggest a compromise so languages are released when they reach a “critical mass”. For example, release a language when:

- A minimum percentage of strings is translated (eg, 50% or 75%)
- The homepage has been fully translated.
- The landing page of each section has been fully translated.

When we decide a translation is ready to go live, we add it to the Astro configuration to build it along with the English version.