[polylang] How can I set defaullt value to polylang translations ?

You can do something close to:

global $polylang;
$language = $polylang->get_language('en'); // example here for English
$mo = $polylang->mo_import($language); // all string translations in $language
$mo->add_entry($mo->make_entry('string to translate', 'default translation')); // add the default translation
$polylang->mo_export($mo, $language); // save translations in the database

Hi chouby . Thanks for your answer. I wrote this yesterday to manage translation import when setting up the site.
I my case I need french and english translation :

<?php
require_once( ABSPATH.'wp-content/plugins/polylang/include/admin-base.php');
require_once( ABSPATH.'wp-content/plugins/polylang/include/admin.php');

/**
 * Manage translation object for initial import. Need the string reference, the french translation and the english translation
 *
 *
*/
class Translation
{
	public $termReference ;
	public $termTranslationFr ;
	public $termTranslationEn ;

	public function __construct($termReference, $termTranslationFr, $termTranslationEn)
	{
		$this->termReference=$termReference ;
		$this->termTranslationFr=$termTranslationFr;
		$this->termTranslationEn=$termTranslationEn ;
	}
}//end of class Translation

/**
 * Manage translation import. Imports Translation objects.
 * This class allows to import translation to polylang backoffice. polylang sets options in wp3_options.
 * Query to see how polylang options : select * from wp3_options where option_name like 'polylang_mo%'
 * This import mechanism his largely inspired by the 2 followings methods of polylang located in wp-content/plugins/polylang/include/base.php :
 * function mo_export($mo, $lang)
 * function mo_import($lang)
 */
class TranslationImporter
{
	private $tableTranslations ; //contain all Translation objects to import
	private $moFr ; //MO object for french translation
	private $moEn ; //MO object for english translation

	private $polylang_mo_fr_code='polylang_mo251' ;
	private $polylang_mo_en_code='polylang_mo253' ;

	public function __construct()
	{
		$this->moEn = new MO();
		$this->moFr = new MO();
		$this->tableTranslations = array();
	}

	/**
	 * adds a Translation object to
	 * @param unknown $translation the array tableTranslations
	 */
	public function addTranslationToImport($translation)
	{
		array_push($this->tableTranslations,$translation);
	}

	/**
	 * import translations from tableTranslations attribute to the french MO and english MO attributes.
	 */
	public function importTranslationToMo()
	{
		foreach ($this->tableTranslations as $row)
		{
			//make_entry('reference string ', 'translation')
			$this->moFr->add_entry($this->moFr->make_entry($row->termReference, $row->termTranslationFr));
			$this->moEn->add_entry($this->moEn->make_entry($row->termReference, $row->termTranslationEn));
		}
	}

	/**
	 * Update polylang options from the mo attributes which has been fill in with the importTranslationToMo method
	 */
	public function updateOptionsFromMO()
	{
		$stringsFr = array();
		foreach ($this->moFr->entries as $entry)
			$strings[] = array($entry->singular, $this->moFr->translate($entry->singular));
		update_option('polylang_mo'.'251', $strings);

		$stringsEn = array();
		foreach ($this->moEn->entries as $entry)
			$strings[] = array($entry->singular, $this->moEn->translate($entry->singular));
		update_option('polylang_mo'.'253', $strings);

	}
}//end of class TranslationImporter

/**
 * This main script imports translation into polylang.
*/
require_once($_SERVER['DOCUMENT_ROOT'].'/wp-load.php') ; //use $_SERVER['DOCUMENT_ROOT'] to refer to WP root while ABSPATH isnt yet set.
require_once(ABSPATH.'wp-content/plugins/international-int/classes/InternationalIntTranslationImporter.class.php');
$start_time = microtime(true); //calcul exec time for fun 

$TranslationImporter = new TranslationImporter();
//add the translations to the importer
$TranslationImporter->addTranslationToImport(new Translation('annuaire', 'annuaire', 'adress book'));
$TranslationImporter->addTranslationToImport(new Translation('vos commentaires', 'c fr ', 'c en'));
$TranslationImporter->addTranslationToImport(new Translation('INTRANET INTERNATIONAL', 'fr ', 'en'));
$TranslationImporter->addTranslationToImport(new Translation('Evénements clients', 'Evénements clients', 'customers event'));
$TranslationImporter->addTranslationToImport(new Translation('ref', 'fr ', 'en'));

$TranslationImporter->importTranslationToMo(); //generate MOs in the importer
$TranslationImporter->updateOptionsFromMO(); //update WP options from MOs importers

echo 'end of translation import. execution took : '.(microtime(true) - $start_time).' seconds.';

greetings,
ben