I stumbled a bit around traversing the hash, but hopefully this helps.

#!/usr/bin/perl

use File::Basename;
use Data::Dumper;

my %LANGUAGE;

foreach my $language_file ( <*.language> ) {
  my $basename = basename($language_file, qw( .language ));
  my $uc_basename = uc( $basename );

  open( FILE, $language_file ) or die "Unable to open $language_file!\
+n$!\n";

  $LANGUAGE{$uc_basename} = {};

  while ( <FILE> ) {
    chomp;

    my $hash = $LANGUAGE{$uc_basename};

    if ( /\$LANGUAGE{$uc_basename([^}]*)}\s*=\s*(.*)$/i ) {
      my $keyword = $1;
      my $value = $2;
       
      if ( $keyword ) {
         my @sub_hashes = split(/_/, $keyword); 
         
         # shift the first one off because it will be empty;
         shift @sub_hashes; 
         foreach ( @sub_hashes ) {
          $hash->{$_} = {} unless exists $hash->{$_};
          $hash = $hash->{$_};
          }
      }  
      $hash->{'value'} = $value;
    }
  }

  close( FILE ) or die "Oh no! COuldn't close $language_file!\n$!\n";
}

print Dumper( \%LANGUAGE );
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