PHP exec change encoding

I need to address UTF-8 filenames with the php exec command. The problem is that the php exec command does not seem to understand utf-8. I use something like this:

echo exec('locale charmap');

returns ANSI_X3.4-1968

looking at this SO question, the solution lookes like that:

echo exec('LANG=de_DE.utf8; locale charmap'); 

But I still get the same output: ANSI_X3.4-1968

On the other hand - if I execute this php command on the bash command line:

php -r "echo exec('LANG=de_DE.UTF8 locale charmap');"

The output is UTF-8. So the questions are:

1. Why is there an different result be executing the php command at bash and at apache_module/web page?
2. How to set UTF-8 for exec if it runs inside a website as apache module?