Creating GIN index throws "function does not exist" error

My table has the following columns:

• content_vector tsvector
• lang VARCHAR(50)

I'm struggling with creating a GIN index.

Approach one: Explicit type casting

CREATE INDEX pages_vector_ix ON pages USING GIN (to_tsvector(lang::regconfig, content_vector));

This creates the following error despite using an explicit type cast as described in this post:

function to_tsvector(regconfig, tsvector) does not exist

Approach two: Altering column's type

It should also be possible to change the column type to reconfig according to this post:

ALTER TABLE pages ALTER COLUMN lang TYPE reconfig USING lang::reconfig;

Now I'm getting an error because apparently I've stored languages in the database that can't be used as a text search configuration, for example:

text search configuration "afrikaans" does not exist

This error makes me question if it's possible to set a GIN index at all if there are potentially languages stored in the database that are not supported by Postgres.

Additional information

select * from pg_catalog.pg_ts_config;

results in

  cfgname   | cfgnamespace | cfgowner | cfgparser
------------+--------------+----------+-----------
simple     |           11 |       10 |      3722
danish     |           11 |       10 |      3722
dutch      |           11 |       10 |      3722
english    |           11 |       10 |      3722
finnish    |           11 |       10 |      3722
french     |           11 |       10 |      3722
german     |           11 |       10 |      3722
hungarian  |           11 |       10 |      3722
italian    |           11 |       10 |      3722
norwegian  |           11 |       10 |      3722
portuguese |           11 |       10 |      3722
romanian   |           11 |       10 |      3722
russian    |           11 |       10 |      3722
spanish    |           11 |       10 |      3722
swedish    |           11 |       10 |      3722
turkish    |           11 |       10 |      3722