I got this instead:
rstudio-user@88c879295fe4:/cloud/project$ tlmgr --usermode init-usertree
(running on Debian, switching to user mode!)
tlmgr: action init-usertree returned a warning.
rstudio-user@88c879295fe4:/cloud/project$ tlmgr --usermode install spanish.ldf
(running on Debian, switching to user mode!)
/usr/bin/tlmgr: Initialization failed (in setup_unix_one):
/usr/bin/tlmgr: could not find a usable xzdec.
/usr/bin/tlmgr: Please install xzdec and try again.
tlmgr: Couldn't set up the necessary programs.
Installation of packages is not supported.
Please report to texlive@tug.org.
We will look into making xzdec available.