Your problem is IMHO, that you locale is already in utf8. This means that your env var is in utf8 but your $testString is in latin1. If this is the case you need to use Encode;. And update the bytes from your environment to utf. 
$fileAsked = Encode::decode(utf8 => $ENV{'aa'});

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Boris

In reply to Re: problems matching umlauts in env vars by borisz
in thread problems matching umlauts in env vars by december

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