another way to register widget's title and text

<?php
// this part
$title = apply_filters( 'widget_title', $instance['title'] );
        $content = apply_filters( 'widget_content', $instance['content'] );

// change into

$title = icl_t( 'my_plugin_name','my_widget_title', $instance['title'] );
$content = icl_t( 'my_plugin_name', 'my_widget_content', $instance['content'] );

// in wp-admin > widgets confirgure this widget and visit at least once front end page which displays widget.
// after that go to wpml > st