The ideal code I'm dreaming about probably looks like following:

# if any non-english language chara in the line
if ( $line =~ /[[:non-english_chara_class:]]/g ) {
    print "Keep the content as is";
}
elsif ( $line =~ /[[:garbage_chara_class:]]/g ) {
    # do some filtering
}
[download]

Your if/else block wouldn't work as expected, since the if-condition would always be true as long as there is one character pertaining to the [[:non-english_chara_class:]] among any number of [[:garbage_chara_class:]] characters. Perhaps match the garbage first and remove it.

Apart from that, it is entirely possible to define your own "named" character classes using the (yet experimental) (?[ ]) regular expression construct, available from perl v5.18 onwards (see Extended Bracketed Character Classes in perlrecharclass):

no warnings "experimental::regex_sets";
my @expressions = (
    "Depósito Centralizado",
    "voilà: a word with an accent grave",
    'this is plain ascii',
    'gräßliches Tröten',
);

my $acute = join'', map { chr $_ } (193,201,205,211,218,221,225,233,23
+7,243,250,253);
my $grave = join'', map { chr $_ } (192,200,204,210,217,224,232,236,24
+2,249);

my $spanish = "[:ascii:] + $acute";
my $french = "$spanish + $grave";

for (@expressions) {
    if (/^[[:ascii:]]+$/) {
        print 'ascii';
    } elsif (/^(?[[$spanish]])+$/) {
        print 'spanish';
    } elsif (/^(?[[$french]])+$/) {
        print 'french';
    } else {
        print 'unknown';
    }
    print ": $_\n";
}
__END__
spanish: Depósito Centralizado
french: voilà: a word with an accent grave
ascii: this is plain ascii
unknown: gräßliches Tröten
[download]

The above character classes are far from complete, but you get the meaning ;-)

<update> correct ascii test and move to first test </update>

... no code tags ..

start using code tags please  <c> code here </c>

Oops... sorry I missed the tags for the code...

I have updated the thread now, hope it looks easier to read.

Thanks

Further to shmem's post above:
If it's just a question of translating text from single seventh-bit-set characters to some kind of pure-ASCII representation, it's possible to do this in one swell foop. The process of defining the translations can be a bit tedious, but it's done just once (update: and could even be done in a module for general inclusion). Note that in the code below, the German eszett/sharp-s "ß" translates to the "ss" ASCII letter pair. See also the possibly useful discussion of something like this for multi-byte Unicode sequences in the recent threads Read RegEx from file and particularly Re: Read RegEx from file.

use warnings;
use strict;

use Data::Dump qw(dd);


my @acutes = qw(193 A  201 E  205 I  211 O  218 U  225 a  233 e  237 i
+  243 o  250 u  221 Y  253 y);
my @graves = qw(192 A  200 E  204 I  210 O  217 U  224 a  232 e  236 i
+  242 o  249 u);
my @others = qw(228 a  246 o  223 ss);

my %xlate = (@acutes, @graves, @others);
# dd \%xlate;  # FOR DEBUG

my ($search) =
    map  qr{[$_]}xms,
    join '',
    map  sprintf('\%03o', $_),
    keys %xlate
    ;
# dd $search;  # FOR DEBUG

while (my $line = <DATA>) {
    chomp $line;
    $line =~ s{ ($search) }{$xlate{ord $1}}xmsg;
    die "non-ascii in '$line'" if $line =~ m{ [[^:ascii:]] }xms;
    print "'$line' \n";
    }


__DATA__
spanish: Depósito Centralízado
french: voilà: a word with an accent gravè
vanilla: this is plain ascii
other: gräßliches Tröten
[download]

c:\@Work\Perl\monks\sylph001>perl xlate_to_ascii_1.pl
'spanish: Deposito Centralizado'
'french: voila: a word with an accent grave'
'vanilla: this is plain ascii'
'other: grassliches Troten'
[download]