That's not what legal tender means in all parts of the world. For instance, in England and Wales, legal tender has an extremely narrow definition - it means that a law court has to accept it for the payment of a debt. Legal tender doesn't apply to people who aren't law courts, and legal tender only applies to past debt - it doesn't apply to future payments such as a purchase at a shop.

It looks (from the news articles) that it has a broader definition in El Salvador, but unless one is an expert in that country's law, it would be best not to make claims about it. If someone is an expert, I'd love to hear what the actual facts are.