undefined_object language “…” does not exist — 42704

Symptoms

A function or statement referenced a procedural language that is not installed. PostgreSQL raises SQLSTATE 42704 (undefined_object).

• The named language isn’t available in this database.
• Common when creating a function in plpython/plperl without the extension.
• Languages are installed per database.

What the server log shows

ERROR:  language "plpython3u" does not exist
HINT:  Use CREATE EXTENSION to load the language into the database.

Why PostgreSQL raises this — what the manual says

the CREATE LANGUAGE reference (Description):

“CREATE LANGUAGE effectively associates the language name with handler function(s) that are responsible for executing functions written in the language.”

Procedural languages must be loaded into a database before functions can use them. Referencing one that isn’t installed cannot be resolved, so PostgreSQL reports 42704.

Common causes

• The language extension wasn’t installed in this database.
• A typo in the language name.
• The language package isn’t present on the server.

How to fix it

1. Install it: CREATE EXTENSION plpython3u; (requires the OS package).
2. List languages: \dL or query pg_language.
3. Confirm the language package is installed on the server.

Related & next steps

• SQLSTATE 42704 — Undefined Object (full reference)
• Message: extension does not exist
• Glossary: Procedural language

Reference: PostgreSQL 18 — CREATE LANGUAGE.