invoices: choose language and duration format (#1438)

src/Invoice/InvoiceModelHydrator.php

@@ -0,0 +1,15 @@
+<?php
+
+/*
+ * This file is part of the Kimai time-tracking app.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Invoice;
+
+interface InvoiceModelHydrator
+{
+    public function hydrate(InvoiceModel $model): array;
+}