Nice pull request and good shot at trying to keep tests green! Here is my feedback:

• The language country from the Language report is detected from the language code itself rather than the actual country of the user. So the data already archived in Piwik is good enough: it gives us the full list of all accept languages including language country codes.
  • Changes in Archiver.php are not needed and can be removed.
• From the existing archived data you can run the datatable GroupBy filter and then group by detected { language code, language country }
  • eg. the GroupBy filter would call a function to extra language en and country bb from the accept language en-bb
  • in case there is no country detail eg. language code is pl then simply write Polish (pl) (instead of current Polish - Poland - (pl-pl))
  • eg. if we have both fr and fr-be then the datatable will show both rows French (fr) and French - Belgium (fr-be) (and not French - France (fr))
• in label column to keep it simple, write Arabic - Qatar (ar-qa) instead of Arabic - Qatar - (ar-qa)
• Integration test look good! some feedback:
  • maybe generate more than 1 visit for some languages so we confirm that algorithms work when nb_visits > 1
  • since we don't use the user country location code in the code, it can be removed from the test as well

let me know if you need help with making build green, travis uploads all processed artifacts which you can download and put in expected/ folder in case it's slow to run tests locally. See https://github.com/piwik/piwik/blob/master/tests/README.md#build-artifacts

as soon as you make those changes and build is green I'll be able to merge. Cheers!

Ok, all tests are green. Could you look at this ?

Review

• excellent! the code is more simple now and just makes sense.
• the PR includes the file chmod changes from 644 to 755 -> can you revert the permission changes somehow, configure git with git config core.fileMode false (source)
• otherwise looks good and happy to merge!

Kuddos @vox3r for this work.
It will be released tomorrow in 2.7.0 to thousands of users. this is a very good start to the project!