Ummm... okay, a variable variable is 'aac' in this example:
<dtml-call "REQUEST.set('aac','yyy')">
<dtml-call "REQUEST.set('varname','aa'+'c')">
<h2><dtml-var "_['aac']">
<h2><dtml-var "_[varname]">
So going back to my original example, it would look like this:
<dtml-call "REQUEST.set('varname','long_date_'+ENV_LANG_VAR)">
<dtml-var "_[varname]">
So you get rid of the whole
<dtml-if><dtml-elif><dtml-elif>...<dtml-else> chain. Everything in
just two lines.
Not that I like self-modyfing code. But if it's short, it's not that bad.