Change asset upload path based on locale
{craft.locale} won't work because the single curly brace syntax is short for {{object.craft.locale}} where object is the element that is currently being edited (in your case, the entry).  You can read more about that here: https://craftcms.com/docs/assets-fields#dynamic-subfolder-paths

Your screenshot shows the double curly syntax, though (which should work fine).

Alternatively you could use {locale}, which would translate into {{object.locale}}, which would be the currently locale of the entry.