Similar issue after creating a new instance of 5.0.2. During the install process I forgot to select a default language using the installation wizard. When I started interacting with the host settings of the initial portal (Host > Portals) the host/portal settings did not have a language assigned and nothing existed in the default language field of the "Advanced Settings > other settings" section. The missing default language created an error message similar to the ones in this post when attempting to update settings changes. The post Boonew quoted below helped a lot!

NOTE: But...... I had to make one additional step to make this work for my similar problem. I had to add an additional language in order to propogate the default language field of the host and portal. Although through the portal admin a language existed, through the host > portal, the language was blank, until I added two languages. In my case English (UK) and English (US)...  Hope this helps someone with this issue.

Thanks Boonew.

Thanks to Boonew, i've solved in my 2 dnn 5.1.2 instance

But in another one i cannot use this method because under ADMIN menu there's no Languages Item !

Someone can help me ??

Blondie

I am having the same issue. There are no languages listed. When I try to add English (United States) I get an error saying that it has already been loaded (index reference error). It does not show on the drop down in other settings or in the Available Locales on the Languages page. Please help.

Thanks,

Rob