But i think you are talking about recognition as an official currency.
Well this is not going to happen, at least unless the bank and the goverments find a way to control it and eliminate the anonymity.
Some countries already official recognized it as a currency (Japan) or as a Commodity (USA) but still there are a lot other countrues that BTC transaction are illegal (https://en.wikipedia.org/wiki/Legality_of_bitcoin_by_country_or_territory)
Isn't it also a problem that they cant get taxes over it?
One of the many problems, yes. If you didn't bought bitcoins using fiat/ ( using your bank accounts), they have no clue how much bitcoin you own.
In most western countries these days they do ask you how assets in BTC you own ( basically bitcoins + altcoins), I don't know how they're checking it.
It seems very hard.
I guess it's impossible right? They can't trace Bitcoins so they can only see that you have bought some. Maybe they can tax the transaction of BUYING BTC. But it should stop there. You could always say that you have already spend the BTC's and they wouldn't verify if that's true or not since all the wallets and the transactions are not saved on a bank that they can request to give insight in. But the transaction of buying the coins, that would be taxable, right?