If you truly understood how Bitcoin works, or even considered it, then you would definitely understand that there is NO need for Bitcoin to be "Legal Tender" to be used as a currency.
That's the essence of Bitcoin. It doesn't need any approval, it doesn't need permission, from any governing entity to be used for transacting with one another.
People are still able to use Bitcoin even it is Ilegal in their nations but it is obviously not recommended to do actions against governments especially existing laws in your country.
By making this example, I meant there is no absolute barrier to prevent people globally using Bitcoin blockchain. If people can use it in countries consider it as illegal. It is more easily to access and use Bitcoin in countries where Bitcoin is Legal or Alegal.
Generally, no reasons of unable to use Bitcoin if there is no Bitcoin Legal Tender in your nation.