I was there a few weeks ago. You will have a very hard time using only Bitcoin. I was only able to spend Bitcoin in El Zonte. Some places had signs saying they accept Bitcoin, but when I asked to pay with it they said no. At one place they tried to use the Chivo wallet and it did not work with my Phoenix wallet.

The truth is Bitcoin is not being promoted and supported very well by the government despite them making it legal tender. Most people don't want to bother with it because people that want to pay with Bitcoin are extremely rare and it's not worth the hassle. If you want to go to El Salvador I would recommend bringing lots of USD cash, especially smaller bills and dollar coins. If you're hoping to spend only Bitcoin then you will find your options extremely limited.  

 Thank you for the detailed answer, appreciate it.