Chouby on "[Plugin: Polylang] Getting string translation on custom language"

Hi!

Yes. By default only one language is loaded by WordPress (and Polylang does not load other for performance reasons).

You can inspire yourself from this to get translated strings registered with pll_register_string:

global $polylang;

foreach ($polylang->model->get_languages_list() as $language) {
	$mo = new PLL_MO();
	$mo->import_from_db($language);
	$translation = $mo->translate($my_string);
	...
}