Passing column name to a function at runtime

I have a language table (translations) with column names which are the
language for the items in that column:

english spanish german etc.

I am joining that table to another table on an integer id.

I am trying to write a type statement and function where the name of the
column is passed into the function. That language name appears in the
select portion of the query:

#type

CREATE TYPE catCats AS (classid integer, varname text, color text, lang
text);

#function

CREATE OR REPLACE FUNCTION listCategories(text) RETURNS SETOF catCats AS
$$

SELECT DISTINCT(classid), varname, color, $1

FROM span_classes

LEFT JOIN translations ON translations.lid = span_classes.descript_tid

GROUP BY classid, varname, color, $1

ORDER BY classid ASC;

$$ LANGUAGE SQL;

#using the function

select * from listCategories(english);

If I pass in english or "english" it says column does not exist. If I
pass in 'english' I get the literal english in my result set.

If I substitute the literal english (with no quotes) in place of the $1
in the function, the query returns the english values from the
translations table correctly.

I've tried bytea for the datatype, as well as a table alias. I don't
know the language column until runtime so I can't code it in the
function.

What am I doing wrong?