Here is hosted the PKGBUILD script for the current Metacall CLI, it also inside the AUR under the name metacall-git.
The variable METACALL_LOADER_language=on can be set in order to build with support of a specific loader.
Supported loaders are found in the following documentation.
Using your favorite AUR helper you can install the package :
sudo paru -S metacall-git
sudo aura -Axc metacall-git