WIPO Copyright Treaty (WCT) protects software and databases with a national treatment similar to Patent or Trademark. I say use Contracting parties in desktop mode and anything with Accession or Ratification and an in force date before now you can copyright software in. There is TRIPS and World Trade Organization (WTO) which governs this but with WIPO Copyright Treaty is only officially protected stuff for software. For national contacts and getting how to have copyright in a specific place, WIPO directory is good. That lists all intellectual property offices you should contact for copyright.
You can also patent software. Patents are shorter lived but broader in what is protected. With that, Patent Cooperation Treaty (PCT) helps. Thus are PCT members. I think same as WCT, Contracting parties, etc.. You will need an international patent thing to start but need to nationalize, file or otherwise make valid, in other countries to be protected there. Again WIPO directory is good, it lists concerned intellectual property (IP) offices of countries and some patent and copyright offices.
Consult a lawyer or attorney for additional information. It is a good idea to consult one before going public with your software. There are discounts for unpublished works as opposed to published ones. You may only need one lawyer or attorney but note that law is national to an extent and so local and international laws and stuff apply. I am not responsible for your actions based on this. I recommend always having either copyright or patent of things you intend to sell or otherwise profit from unless it is open source, free, or like that.