Creating paragraph entities and adding to a node
I have a similar function and would recommend that if you already know what language your node is, you capture it from the node and use it for the language in the paragraph field. I only had 1 language to worry about but you could easily replace LANGUAGE_NONE('und') with the appropriate language code from the node.

$paragraph = new ParagraphsItemEntity([
  'field_name' =&gt; $host_field_name,
  'bundle'     =&gt; $para_bundle,
]);
$paragraph-&gt;is_new = TRUE;
$paragraph-&gt;setHostEntity('node', node_load($this-&gt;node-&gt;nid));
$paragraph-&gt;field_long_text[LANGUAGE_NONE][0]['value'] = $field_content;
$paragraph-&gt;field_long_text[LANGUAGE_NONE][0]['format'] = 'wysiwyg';
$paragraph-&gt;save();