fish is nice but I've ran into too many issues where some weird shell command / script I find online is expecting to be in bash and I have to switch out of fish, so its hard for me to switch.
As long as they don't need to be sourced, you can just add a shebang for bash at the top of the scripts and run them via bash.
If they do need to be sourced, you can use bass: https://github.com/edc/bass