I just tried to test something with basic webcontent, but to my surprise, webcontent display didn't show my content. I could enter whatever I want in the content field of the webcontent, the Webcontent display didn't show it.
I believe, Non US Language default language causes that issue.
Steps to reproduce:
1) Fresh install of Liferay
2) In Configuration: Choose German Language as default language
3) Start Liferay
4) Add Webcontent display to page
5) Click + icon in Webcontent display
6) Fill out the fields, please note that the input default language is set to "German". Enter "XXXX" in content field.
7) Save content & return to page
Expected result: XXXX is shown in Webcontent display
Actual result: Webcontent display stays empty.
Note: Adding an US translation AND switching user language to US showed the content for me.