Leftover work discussed on T232410: Newcomer tasks: add language question to welcome survey

In T232410#6377157 @MMiller_WMF wrote:
[...] Suppress language variants from the list, such as "en-gb" and "ku-arab"

To recap, this task is to show only the "main" language and not its variants, for selection. For e.g., show only English, and suppress British English and Canadian English.