$ cat script.pl                                                                                                                                                                                                                              
#!/usr/bin/perl                                                                                                                                                                                                                              
                                                                                                                                                                                                                                             
use strict;                                                                                                                                                                                                                                  
use warnings;                                                                                                                                                                                                                                
use XML::Twig;                                                                                                                                                                                                                               
                                                                                                                                                                                                                                             
{                                                                                                                                                                                                                                            
        my $twig = XML::Twig->new(                                                                                                                                                                                                           
                twig_handlers => {                                                                                                                                                                                                           
                        q{Text[@Id="98"]/Language} => sub {                                                                                                                                                                                  
                                $_->subs_text( qr{(?ix)su \s+ saldo \s+ es (?=\s)}, 'Your Balance' );                                                                                                                                        
                        }                                                                                                                                                                                                                    
                },                                                                                                                                                                                                                           
                pretty_print => 'indented',                                                                                                                                                                                                  
        )->parsefile( shift )->print;                                                                                                                                                                                                        
}                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
$ perl-5.14.2 script.pl infile                                                                                                                                                                                                          
<root>                                                                                                                                                                                                                                       
  <Text Id="98">                                                                                                                                                                                                                             
    <Language id="1">Your Balance $mainAccountBalance1Tiene ademas $dedicatedAccount1Balance1 mensajes de texto</Language>                                                                                                                   
    <Language id="2"></Language>                                                                                                                                                                                                             
    <Language id="3">Your Balance $mainAccountBalance1Tiene ademas $dedicatedAccount1Balance1 mensajes de texto</Language>                                                                                                                   
    <Language id="4">Your Balance $mainAccountBalance1Tiene ademas $dedicatedAccount1Balance1 mensajes de texto</Language>                                                                                                                   
  </Text>                                                                                                                                                                                                                                    
  <Text Id="96">                                                                                                                                                                                                                             
    <Language id="1">Su saldo es $mainAccountBalance1.</Language>                                                                                                                                                                            
    <Language id="2">Su saldo es $mainAccountBalance1.</Language>                                                                                                                                                                            
  </Text>                                                                                                                                                                                                                                    
  <Text Id="12">                                                                                                                                                                                                                             
    <Language id="1">Su saldo es $mainAccountBalance1.</Language>                                                                                                                                                                            
    <Language id="2">Your balance  $mainAccountBalance1.</Language>
  </Text>
</root>