'Embed in post' is not translated:

[inliquid]

See the screenshot:

At the same time 'Delete' is translated.

Here is 'definitions.Attachments.php'

$definitions["Attach a file"] = "Прикрепить файл";
$definitions["Drop files to upload"] = "Перетащите сюда файлы для загрузки";
$definitions["Embed in post"] = "Встроить в сообщение";
$definitions["message.attachmentNotFound"] = "Этот файл вам недоступен. Возможно, он отсутствует, либо у вас нет прав для его просмотра";

[inliquid]

Small comment -> translation doesn't work only when you just upladed new file, when you edit existing post, it works.

[inliquid]

/addons/plugins/Attachments/resources/attachments.js:39

.html('<a href="#" class="control-delete" title="'+T("Delete")+'" data-id="'+responseJSON.attachmentId+'"><i class="icon-remove"></i></a> <strong>' + file Name + '</strong> <span class="attachment-controls"><a href="#" class="control-embed" title="'+T("Embed in post")+'" data-id="'+responseJSON.attachmentId+'"><i class="icon-external-link"></i></a></span>');

Please consider also adding quotes to -> "'+T("Delete")+'"