If I've understood you correctly, you need [^#]+ to match ungreedily by using the ? quantifier: 
my %langhash;
$langhash{'dígito verificador incorrecto.'} = 'digit incorrect.';

my $string = '(5/4/07 4:24:03 PM CDT) 1473721:   ##   dígito verificad
+or incorrecto.   ##pp';

if ($string =~ s/##\s*([^#]+?)\s*##/##$langhash{$1}##/) {
  print "$langhash{$1}\n";
  print "/$1/\n";
  print $string;
}

[download]

Prints: 

digit incorrect.
/dígito verificador incorrecto./
(5/4/07 4:24:03 PM CDT) 1473721:   ##digit incorrect.##pp

[download]

Is that what you're after?

In reply to Re: substitution not working correctly by FunkyMonk
in thread substitution not working correctly by qnguyen

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