Which countries do not have an official language?

According to Henry Hitchings Language Wars (2011) these nations do not currently have an official primary language:
  • UK see here
  • USA though 20 states now have an official language — see here
  • Australia Over 80% speak English but there is no official national language.
  • Pakistan Urdu became official language in 2015 but  only spoken by 8% of population.
  • Ethiopia Amharic is official language but most spoken is Oromo
  • Somalia
  • Eritrea 
  • Costa Rica

Why these countries?
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