If by legalize you mean that banks will have to make bitcoin an officially recognized means of payment, than I have a bad news for you, it will never happen No central bank will allow itself to loose the control over currency of any given country. No government will agree to utilize and merge its finance with technology of unknown origin.
Good news is that we, the people, can. Bottom-up initiative is way better anyway. Start to use crypto in transactions between friends and relatives, if you own a e-shop use it as well and voila, bitcoin accepted all over the place.

Yes! In fact Bitcoin is already being used in other countries as a legal means to purchase or buy items and even services. Bitcoin is already being acknowledged as a legal means of payment.

With such slow speed of transactions, it will never become a popular payment method

Could you point us to the source of this news? It would be huge, in fact so huge that I can't imagine, basically hard to believe.
Maybe we have some sort of misunderstanding here, by recognition as a legal way of payment, I mean situation where a shop keeper has no right to refuse you making a purchase with bitcoin. By refusing he is in violation with the law, and faces fine or prison time. This is how things are with fiat money now. There are some derogations from it like legal age in case of alcohol etc. Anyway source please

I think the sooner the bitcoin also becomes a method of payment for the world. I believe that would be true because there were so many countries Recognizing the bitcoin

Bitcoin is the brand, the name, the future. It will always be a store of value, very limited supply and it tradable against all other coins on exchanges. So it will continue to grow in value.

Bitcoin Cash on the other hand, has faster transactions, lower fees and is more likely to be adopted for day to day use. As it is partnered officially with Bitcoin it will continue to grow in popularity.

The massive adaption will make bitcoin as a popular payment because that is only the way that i believed that will work because as long as a lot of businesses like stores in mall or even outside the mall, as long as they are using bitcoin as a mode of payment then it will have an exposure to the customers where they might be interested in investing or using it also.

what about transaction fee? you can say that bitcoin is a good method of payment because of all three things, but of course people using a particular payment method will first see the cost fee first? if there are other cheaper payment methods they will certainly choose another

because bitcoin is the parent of the currency crypto and bitcoin also its price is expensive in comparison with other coins.

I very much doubt that bitcoin will sometime be used for payments. For these purposes, there are more advanced cryptocurrencies. People prefer bitcoin "hold".