In 2021 they adopted it as legal tender [1]. Finance observers such as patio11 have commented "Tether's interactions with El Salvador might be the boldest Bond villain plot ever executed in real life. [..] They're using a sovereign nation as the cash-based business to intermix their dirty funds flows in, and daring the feds to see what happens if they cut them off." [2]

[1] https://en.wikipedia.org/wiki/Bitcoin_in_El_Salvador

[2] https://twitter.com/patio11/status/1493033725524799489

> El Salvador became the first country in the world to use Bitcoin as legal tender, after having been adopted as such by the Legislative Assembly of El Salvador in 2021.

https://en.wikipedia.org/wiki/Bitcoin_in_El_Salvador

El Salvador very publicly invested in bitcoin for the country's future. It didn't go well.

Seems the president, Nayib Bukele, is into Bitcoin: https://www.nytimes.com/2022/07/05/world/americas/el-salvado...

Also, the first linked source on each "buy" on the IsElSalvadorUp page is a tweet from the president announcing that they've bought more BTC.

The head of state declared BTC legal tender last year (ES' official currency is the USD). ES has been accumulating BTC since then, even as the price continues to drop.

Questions like this can be answered by searching "El Salvador bitcoin".