Content Manager - Add New Content issue when language field is set to "All" option

Current behavior

When clicking on "Add New Content" from the search content screen while having the "All" option selected for the language drop down, no language shows as selected in the Add/Edit content screen. The content can be saved and published without specifying the language, and the content gets assigned language_id = 0 in the database.
When searching for the new content created, it get's displayed under "All" language, and there's no flag associated to it.

Proposed behavior

The language field should be mandatory, or at least the default language should be assigned to the content if the Add/Edit screen is reached having "All" as the language selected.

To reproduce the error:

1. Go to the search content screen
2. Select the option "All" for language
3. Click on "Search"
4. Click on "Add New Content"
5. Enter the required fields without touching the language drop down
6. Save and publish
7. Select "All" for language again in the search content screen
8. See the new content showing up without a flag

This is what you see in the database for the contents created without specifying the language:

opensource_12=# select text1, language_id from contentlet where structure_inode = '6002';
 text1 | language_id
-------- +-------------
 test 2 | 0
 test 3 | 0
 test 5 | 0