[ZendTo] problem with changelocale.php

[patpro]

Hello,

I've installed ZendTo on my server few days ago, and I have a problem with changing languages: when I use the language menu and select a language, the page become blank (not a single html line). Error logs for PHP read:

[26-Dec-2018 00:12:05 Europe/Paris] PHP Warning:  include(zendtoindex.php): failed to open stream: No such file or directory in /patpro/hosting/zendto/www/changelocale.php on line 153
[26-Dec-2018 00:12:05 Europe/Paris] PHP Warning:  include(): Failed opening 'zendtoindex.php' for inclusion (include_path='.:/usr/local/share/pear') in /patpro/hosting/zendto/www/changelocale.php on line 153

I guess a "/" is missing in "zendtoindex.php" but I can't find a way to correct that. I'm running ZendTo 5.15-1, installed from ZendTo-5.15-1.tar on a FreeBSD server (php 7.2).
Relevant Apache config: 

353     Alias /zendto "/patpro/hosting/zendto/www"                                                                                                                                     
354    CacheDisable /zendto
355     <Directory "/patpro/hosting/zendto">
356       Options Indexes FollowSymLinks MultiViews
357       AllowOverride None
358       Require all granted
359 
360       RewriteCond %{REQUEST_FILENAME} !-d
361       RewriteCond %{REQUEST_FILENAME}\.php -f
362       RewriteRule ^(.*)$ $1.php
363 
364       php_admin_value memory_limit 300M
365       php_admin_value max_execution_time 28800
366       php_admin_value max_input_time 28800
367       php_admin_value post_max_size 5000M
368       php_admin_value upload_tmp_dir /patpro/hosting/zendto-data/incoming
369       php_admin_value upload_max_filesize 5000M
370       php_admin_value max_file_uploads 200
371     </Directory>

Thanks,
patpro