There are instructions in the manual how to retrieve all information with psql:
12.10. psql Support
Information about text search configuration objects can be obtained in
psql using a set of commands:\dF{d,p,t}[+] [PATTERN]
In particular:
List text search dictionaries (add
+for more detail).=> \dFd
There is more, read the manual.
Ultimately, possible parameter values for to_tsvector(), to_tsquery() et al. are defined by entries in the system catalog pg_ts_config, from where you can get the definitive list. As of Postgres 14:
test=> SELECT cfgname FROM pg_ts_config;
cfgname
------------
simple
arabic
armenian
basque
catalan
danish
dutch
english
finnish
french
german
greek
hindi
hungarian
indonesian
irish
italian
lithuanian
nepali
norwegian
portuguese
romanian
russian
serbian
spanish
swedish
tamil
turkish
yiddish
(29 rows)
But more can be added.