Can not add new languages in OpenCart 2.2.0.0. The "code" dropdown only has "en-gb" value

Question

I am trying to localize a new OpenCart website. I've download the language in question and extracted it under /catalog/language/[xx] (the two letter lang code of the custom language).

However, when I go to Gear menu->Localization->Languages and click "Add new":

The "Code" dropdown only has the "en-gb" value:

Adding another language with the same "Code" is impossible, because it generates an error.

Answer 1

Apparently, instead of unzipping everything from the language pack archive under category/language/[xx] I had to unzip the individual directories from the language pack under:

• /admin/language/[xx]/
• /catalog/language/[xx]/
• /install/language/[xx]/

The lang pack's .zip file was neatly organized in this subfolder structure, but I overlooked this fact. I hope this is useful information for future searchers.