Perl skills are irrelevant here. You just need to read the documentation.

my $dom = 'XML::LibXML'->load_xml(IO => *STDIN);
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> update only the alt-title with origin="tilte"

Again, not a Perl skills question. findnodes uses XPath Expressions, so just modify it:

my ($other_title) = $dom->findnodes('//file/body/group/unit/alt-title/
+otherTitle[@origin="tilte"]');
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> the new values will be taken from another file which will contain the same number of lines as the nodes.

Do you know how to read lines from a file? See open and the diamond operator in perlop. For example, I created an input file called 1 with the following contents:

a
b
c
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Then, I created a simple XML file called 1.xml:

<root>
  <one>
    <two origin="a"/>
    <two origin="b"/>
  </one>
  <one>
    <two origin="b"/>
    <two origin="a"/>
  </one>
  <one>
    <two origin="a">old</two>
    <two origin="b">old</two>
  </one>
</root>
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Finally, here's the script that replaces the text in two with origin="a" by the values read from the given file. $. is a special variable that contains the input's line number, you can use it to index the nodes in the XPath Expression:

#!/usr/bin/perl
use warnings;
use strict;

use XML::LibXML;


my $new_values_file = shift;

my $dom = 'XML::LibXML'->load_xml(IO => *STDIN);

open my $in, '<', $new_values_file or die "$new_values_file: $!";
while (<$in>) {
    chomp;
    my ($two) = $dom->findnodes("/root/one[$.]/two[\@origin='a']");
    $two->removeChildNodes if $two->findnodes('text()');
    $two->appendText($_);
}
print $dom;
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Run as

perl script.pl 1 < 1.xml
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($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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Thank you for your reply.

I adapted my code according to your code and it works. However, I have another issue. It doesn't work with all XML files I have. the difference is that the one files has

<xliff version="1.1" xml:lang='en'>

and it works, while the other one has

<xliff xmlns:m="http://www.xxx.com/mxml/2.0" xmlns="urn:xx:names:tc:xml:document:1.2" version="1.2" m:version="2.3" m:level="1">

and it doesn't work.

Moreover, the second file has the structure below.

Here is my code

#!/usr/bin/perl

use 5.010;
use strict;
use warnings;

use XML::LibXML;

my $new_values_file = shift;
open my $in, '<', $new_values_file or die "$new_values_file: $!";
chomp(my @new_values = <$in>);

my $dom = 'XML::LibXML'->load_xml(IO => *STDIN);

my $i = 0;
foreach my $alt_trans ($dom->findnodes('//file/body/group/unit/alt-tit
+le/otherTitle[@origin="title"]')) {
    print $alt_trans->to_literal();
    $alt_trans->removeChildNodes if $alt_trans->findnodes('text()');
    $alt_trans->appendText($new_values[$i]);
    $i++;
}
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And one more question. Why in this file it doesn't work? Because there are blocks of <group> elements? Is my Xpath correct with this structure?

...
<group>
 <unit id="3Ojs1SLwMmEHK8mJ0_dc2:43”>
  <titleEN>{3&gt;19&lt;3}</ titleEN >
  <titleFR>{3&gt;19&lt;3}</ titleFR >
  <alt-title origin="tilte"><otherTitle/></ alt-title>
  <alt-title origin="price"><otherPrice/></ alt-title>
 </unit>
</group>
<group>
 <unit id="3Ojs1SLwMmEHK8mJ0_dc2:43”>
  <titleEN>{3&gt;19&lt;3}</ titleEN >
  <titleFR>{3&gt;19&lt;3}</ titleFR >
  <alt-title origin="tilte"><otherTitle/></ alt-title>
  <alt-title origin="price"><otherPrice/></ alt-title>
 </unit>
</group>
...
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xmlns="urn:xx:names:tc:xml:document:1.2"
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This defines a default namespace. You need to register it and use it in all the XPath expressions. See Re: XML::LibXML & namespaces for details.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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