Document recommended approach to translation (process and technical implementation)

[duncandewhurst]

The translation section of the OCDS Standard Development Handbook comprehensively documents the process and technical implementation of translation in OCDS and OC4IDS. BODS uses a similar approach, so I think that we should document this as the recommended approach in OS4D.

I suggest the following steps:

1. Check for any major differences/extras between BODS and OCDS/OC4IDS. In particular, I think diagrams in BODS are stored as SVG files to enable translation in Transifex.
2. Decide how to integrate the documentation into OS4D (e.g. the existing translation page, new and existing components and patterns etc.)
3. Author the documentation

[duncandewhurst]

Can address #30 at the same time.

[duncandewhurst]

There's a discussion about translating code titles from external codelists in https://opendataservices.plan.io/issues/36472#note-35