One of the probable solution here for El Salvador citizens must be, if they spend for bitcoins for the purpose of using it as a legal tender then they must spend bitcoins as early as possible; it means do not buy bitcoins for month long expenses just buy bitcoins for one or two days' expenses hence short holding may not hurt much. This way they may get chances to escape from wild fluctuations of bitcoins.
Yeah, not sure how their government will take care of their people against extreme volatile days of bitcoin. I mean after the current bull run which may end in December 2021, we may have usual year long bear run in 2022 which might be not suitable for the people who get paid in bitcoin and saving bitcoins for their daily life. Moreover, bitcoin is in initial stage and El Salvador's decision to adopt might be a real time case study for most other countries.