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The EU doesn't control the council as they are independent. But no country has ever joined the EU without first being a member of the council.
The Council of Europe can't make binding laws but it can enforce certain agreements made by European states. It runs the European Court of Human Rights.
The official languages are English and French. Certain bodies also use German, Italian, and Russian.
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The "eastern block" countries didn't start joining until after the fall of communism. Hungary was the first to join in 1990, followed by Czechoslovakia and Poland in 1991, Bulgaria in in 1992 and Romania in 1993.
Czechoslovakia was replaced by Czech Republic and Slovakia following the Velvet Divorce. East Germany never joined because the the former territory basically joined following the reunification of Germany in 1990. Yugoslavia wasn't ever a member. Following the breakup, Slovenia became the first ex-Yugoslav country to join in 1993. The Soviet Union was never a member either. The first former Soviet republics to join were Estonia and Lithuania in 1993. Other former republics joined later on and Russia joined in 1996.
Montenegro was the most recent country to join back in 2007.
The Vatican does have observer status. As does Israel, the USA, Canada, Japan, and Mexico. The council of Europe has observer status with the United Nations.
The death penalty is abolished in member countries. There's criticism of the USA and Japan each having observer status since the death penalty is still in practice.
Again, since the Council of Europe is not the same thing as the EU, Brexit doesn't apply. While the UK is leaving the EU it will remain in the Council of Europe.
Here's a video I found out on YouTube that explains more about the Council of Europe
©Council of Europe