Would you like to create a new language culture set?
For example SimpleTick has the language pack for German: DE
However let's say you are based in Austria, you would like the language to sound more local.
Examples:

de-AT	German - Austria
de-DE	German - Germany
de-LI	German - Liechtenstein
de-LU	German - Luxembourg
de-CH	German - Switzerland

Here's is the full list of Language Culture Names

In this case you should duplicate the entire folder: ~/App_GlobalResources/de/
To create a new version just of Austrian German, call the new folder: ~/App_GlobalResources/de-AT/

Also rename the files inside, for example:
~/App_GlobalResources/de/Backend.de.resx would become ~/App_GlobalResources/de-AT/Backend.de.resx

Then follow this article on updating the resource file.