I found an Ask Tom article explaining that there is not much difference between CHAR and VARCHAR2 in Oracle. It gave the impression that I should use VARCHAR2(4000 BYTE) for every column where I would like to store strings, even for ISO 639-1 language codes, because it does not make any difference.
I know that it makes sense to use CHAR(2) for ISO 639-1 language codes to enforce a basic data constraint. But this is not a sufficient constraint, because it permits storing 'xy' in the column which is not a valid language code. On the other side I pay for this basic constraint with the limitation that I have to change the database if I want to change my application to use ISO 639-2 language codes, which require 3 characters. So I tend to drop the constraint at all from the database level, because it seems to me that the cost is higher than the benefit.
With that in mind, I am wondering if there is any other significant reason why I should not use VARCHAR2(4000 BYTE) for any string shorter than 4000 bytes that I intend to store in an Oracle database?
Tom Kyte also rebuts your proposition here: https://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1145132537055