Eli Zaretskii <eliz@gnu.org> writes:

>> From: Thierry Volpiatto <thievol@posteo.net>
>> Date: Sat, 20 Jan 2024 05:56:11 +0000
>> 
>> 
>> Its read-language-name specify default in prompt but not as DEFAULT arg.
>
> Thanks.  But why is that a problem?

Because Helm needs this info to handle DEFAULT, it can't be aware of the
code running after the completing-read (read-language-name in this
case).
Also using the DEFAULT arg of read-language-name save you the
need to compute DEFAULT just after:

    (if (null language-name)
        (setq language-name current-language-environment))

This piece of code can be removed.

-- 
Thierry