My website has gone far down in Google and i`m trying to understand why

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Rostyslav Chernyakhovskyy: Hi, my website has gone far down in Google and i'm trying to understand why. I've got two language versions /de/ and /ru/. Default language is /de/. If user enters www.dopeless-design(dot)de, he is redirected to www.dopeless-design(dot)de/de/.
  
  But google has indexed both ;
  
  www.dopeless-design(dot)de
  and
  www.dopeless-design(dot)de/de/
  
  Essentially with the same content.
  Can this cause a problem? Can google see it as ;cloaking?
  Can I solve it adding cannonical link (www.dopeless-design(dot)de/de/) to both pages? Or is there a better practice?
  
  Thx
• 
  Chris Smit: If you have identical content at the two places, it is considered Duplicate Content.
  A 301 redirect or Canonical would work.
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  Rostyslav Chernyakhovskyy: +Chris Smit there is 301 redurect. But google has both pages in index
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  Chris Smit: Are you sure it's setup correctly? I've done this as well for one of my sites (a complete site redirect), and the old site is not indexed anymore. +Rostyslav Chernyakhovskyy ;
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  Rostyslav Chernyakhovskyy: Yes, that's the problem. I'm sure, that there is 301 redirect, but sometimes (not always) it appears in index.
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  Chris Smit: +Rostyslav Chernyakhovskyy ;You could try and take one version Offline... and see if your rankings return.