Learn docs how to do it.

Also, Florian DANIEL aka Facyla is created some docs on the french. Perhaps, you can find some usefull information in there.

Thank you RvR , In addition, here are the files that Pascal need to edit. It has been a while since i worked at this plugin. From memory I will try to help you to locate where the language files are. Hopefully one of "these days" I will be able to move all language strings to one file for easier maintenance.

First look for this files and make any changes from English to French.

mod\fb_register_form\views\default\page\layouts\fb_custom_index.php

mod\fb_register_form\views\default\resources\index.php

Then,  make a file called  fr.php  inside language file like this.

mod\fb_register_form\languages\fr.php

Next copy all of the contents from the file called en.php into fr.php

mod\fb_register_form\languages\en.php

<?php

/**
 * User details
 */


return array(
   
    'register:password' => "Enter a combination of at least six numbers,letters (like ! and $).",      
    'register:passwordagain' => "Please Re-enter your Password Again",
    'name' => "Display Name",
    'email' => "Email Address",
    'register:email:address' => "You'll use this email to log in and to reset your password",
    'register:username' => "Please enter your New Username: You'll use it to log in",
);

Finally edit your fr.php with french language for your users.

Here is an example how the above English file should be translated:

mod\fb_register_form\languages\fr.php

<?php

/**
 * French
 */

return array(
     
    'register:password' => "Mot de passe",      
    'register:passwordagain' => "Mot de passe (confirmation)",
    'name' => "Nom affiché",
    'email' => "Adresse email",
    'register:email:address' => "Adresse email",
    'register:username' => "Identifiant",
    
);   

I hope this will  help you started in the right direction...

I'm not sure what exaxtly you are referring to with image compression. Do you mean the creation of the image thumbnails with some optimized settings with regards to image quality/filesize? If so, I'm not sure (though I think rather not) that Tidypics has this functionality in the version compatible with Elgg 1.8 as I think i've added it only later and never backported to the older version.

With regards to upgrading from v1.8.0-rc1 to the latest version of Tidypics compatible with Elgg 1.8 it should be no problem as the image files itself will not get touched. Only some changes in the database are most likely necessary (as done by the upgrade scripts that come with Tidypics - and it should show you on the Tidypics plugin settings page if updates are pending). Nonetheless, I would advice to backup your data directory and database before upgrading as there might even go something wrong when changes are done in the database.

Apart from Tidpics I would definitely advice to upgrade to a more recent Elgg version as soon as possible. Beside Elgg you would also need compatible versions of your plugins, too, to be able to upgrade (I had not the time yet to upgrade all my own plugins to work on Elgg 3 yet). Whereas Elgg 1.8 (and up to Elgg 1.12) gets no support anymore Elgg 2.3 is still supported and would also work with PHP 7 (whereas PHP 5 has reached its end of life, too).