Please find attached my proposal for a guide for translators. This guide would 
probably be a subpage in 'www.freedroid.org/dev-section/'. I wrote it in markdown 
format as I don't know how the website is formatted, but if it uses another 
format just let me know and I'll adapt.

Version 2. Fixed headers' syntax.

Planning on adding:
- instructions to add new translation
- test translations for new languages in the source code
- ... maybe these could be in an advanced page

Some comments on your 2nd proposal:

1/ In "Install Transifex Client", you mention an alternative, consisting on
downloading PO files for each resource.

Even it that's possible, it implies to then combine individuals PO into one
single PO file. Not so easy, so you should rather not mention that alternative.

2/ You can build fdrpg first, and then update translations. So I think that it
could be simpler to explain how to build the game (by referring the dedicated
web page), and then explain how to update a translation:
  cd po/
  make tx-pull
  make update-gmo

This can be done each time a new translation is to be tested...