Which Country Backs Bitcoin as Currency? – In the EU Bitcoin should be treated as currency, at least for tax purposes.
In Japan Bitcoin is now a legal method of payment, I do not know if it is also considered a currency.
Except above, no country is going to back it at least, but some may allow the technology behind it (the blocks) to be able to thrive as this can be used in many things of government, banking, etc. and so on. Bitcoin will be in a direct fight with the rules when it comes to government and cause problems like the national government (of any gov) want control over all the use of money in your country.
Bitcoin may not be controlled by what the Government (s) will put regulations on it in order to limit its use or merely deter use in general.
I think it’s sad that the government is doing this, but I understand that they prefer to control all this is just a waste to them.
While it was accessible in a specific country and people are having fun freely using Bitcoin without any worries that are facing some terms against the law that applies it, then it can consider it as a supported currency.
But in a technical term, if the government of the country actually recognized Bitcoin as legal and can be used as a standard method of payment as Fiat, then it is fully endorsed by that country. To pass it as a legitimate currency, it will descend a lengthy process that will take a long period so it is evident that once it happened, it is already done.