webmaster.google.com: many http 404 / not found errors are reported

-- url of the page with the problem -- : shop.smartgart.com
-- HikaShop version -- : 3.1.1
-- Joomla version -- : 3.7
-- PHP version -- : 5.5
-- Browser(s) name and version -- : Chrome latest
-- Error-message(debug-mod must be tuned on) -- : http 404 not found

Hi, I have changed a few things on shop.smartgart.com a while ago, and now I see that webmaster.google.com reports that around 600 pages are no longer found.
Those pages have URL suffixes like zh/product/3652-.html or en/product/2928-.html.
My understanding is that if those numbers 3652 or 2928 were product_id's, then that link would work - but they are not, and they are not category_id's either. So somehow I must have mislead googlebot.

Question 1:
What type of id could they be, or how can I find where those links are generated in the 1st place?
They are (of course) not part of the shop.smartgart.com/sitemap-google.xml.
Doing a search for e. g. link:shop.smartgart.com/zh/product/3652-.html does no longer work for Google to find out about link sources.

Question 2:
Is there a code snippet somewhere that illustrates how to determine the type of a page from a displayClass or viewClass - like product detail page, category listing, brand listing?

Thanks!