Same error in DNN 5.06.00!
Same fix helps.

Issue "DNN-13936 - Error when editing Language" still open...

When developers will correct an source code?!

I found another problem that caused similar Module initialization issues. I would suggest that users carefully check all the entries under the Languages module definition. These specific errors appeared in my installation (which has been upgraded many times over the years):

I fixed the languages problem. At the Host/Extensions/Languages screen I did a careful item by item comparison of each of the languages components in the language module definition with a site with a working languages module. I found two errors:

The EDITOR key field value was missing from the module definition for the Languages – I added this key to the record and updated it. The LanguageEnabler.ASCX entry for the control (with no key or title) was missing altogether, so I added it with the same settings as in the working site (partial rendering enabled - no key or title).

Once I fixed both of these errors, and then went through and verified all the other settings were uncorrupted I got a working language setup.

We verified that:
• The files themselves are fine
• The module is properly installed in the IIS framework
• The resource files are not corrupt and have valid XML
• We’re working with the right module version
• The Languages module was “installed”

Bit of a challenge finding this one – had to dig deep inside the module definition to sort it all out - hope this helps someone else with the same problem. Note (Installing a working languages.zip module definition over the broken one did NOT fix the SQL records with the settings - we didn't try completely uninstalling then reinstalling the languages module as we had existing language resources that had been customized.