What sama55 mentions is perfectly fine and it will work in Q2A v1.7.0 and below. The thing is that approach has been deprecated as of Q2A v1.7.0 in favor of the new metadata files (explained here http://www.question2answer.org/qa/40745).
In the new approach, you can freely add any directory name under the qa-lang directory but you'll need to add a metadata.json file to the directory. That file is a JSON file that would contain something like this:
"name": "Portuguese - Portugal"
The name attribute just contains the value that you want to see in the combobox when selecting languages.