Something is up with this:
Maybe login to the container and run pg and /dF
var/discourse# ./launcher enter samsaffron
var/www/discourse# sudo -u postgres psql
psql (10.7 (Ubuntu 10.7-1.pgdg16.04+1))
Type "help" for help.
postgres=# \dF
List of text search configurations
Schema | Name | Description
------------+------------+---------------------------------------
pg_catalog | danish | configuration for danish language
pg_catalog | dutch | configuration for dutch language
pg_catalog | english | configuration for english language
pg_catalog | finnish | configuration for finnish language
pg_catalog | french | configuration for french language
pg_catalog | german | configuration for german language
pg_catalog | hungarian | configuration for hungarian language
pg_catalog | italian | configuration for italian language
pg_catalog | norwegian | configuration for norwegian language
pg_catalog | portuguese | configuration for portuguese language
pg_catalog | romanian | configuration for romanian language
pg_catalog | russian | configuration for russian language
pg_catalog | simple | simple configuration
pg_catalog | spanish | configuration for spanish language
pg_catalog | swedish | configuration for swedish language
pg_catalog | turkish | configuration for turkish language
Our install comes with no pg_catalog czech, so your db needs to be configured with a support locale or you need to figure out how to install another catalog.