Very good, i could see the support for languages ​​in Portuguese appears like this

groupinvite:widget:title

Most likely you didn't disable cache before you applied your translation.

During normal operation (= cache ENABLED) all localization arrays will be cached, too. Thus, if you want to apply any changes, cache needs to be DISABLED first.

I tried to create a german language-file (ossn.de.php)

<?php
/**
* Open Source Social Network
*
* @packageOpen Source Social Network
* @author Open Social Website Core Team <[email protected]>
* @copyright (C) SOFTLAB24 LIMITED
* @license OSSN License https://www.opensource-socialnetwork.org/licence
* @link http://www.opensource-socialnetwork.org/licence
*/
$de = array(
'groupinvite:widget:title' => 'Freunde einladen',
'groupinvite:widget:desc' => 'Wähle deine Freunde aus!',
'groupinvite:invite' => 'Einladen',
'groupinvite:sent' => 'Die Einladung wurde verschickt.',
'ossn:notifications:groupinvite' => '%s hat dich eingeladen, der Gruppe <strong>%s</strong> beizutreten.',
);
ossn_register_languages('de', $de);

The result is : groupinvite:widget:title displayed instead the translation. What do I wrong??

Thats great!