You can try from Blizzard_TradeSkillUI.lua:
Code:
--[[ Parent categories ]]--
local categories = { C_TradeSkillUI.GetCategories() };
for i, categoryID in ipairs(categories) do
local categoryData = C_TradeSkillUI.GetCategoryInfo(categoryID);
info.text = categoryData.name;
The name is localized. However, it appears with my brief testing that you need to have opened the Blizzard panel up first before C_TradeSkillUI API actually returns non nil.