Language Manager makes POST request for each element added to project

Description

Steps to reproduce

1. Create the Apply demo website and install EPiServer.Labs.LanguageManager, 3.1.6 version.
2. Create the website for multiple languages.
3. Create a new project.
4. Add the "Languages" gadget.
5. Select the start page.
6. In the "Languages" gadget, click "Add to translation project".
7. Select checkboxes for all child nodes and related content.
8. Click "OK" to add translation.

Expected
Application makes a POST request for each element added to the project.

Actual
Application become unresponsive as it makes POST request for each element added to the project.