Make a list of translation fields
Check titles, descriptions, features, options, availability notices, metadata, and information pages. An empty field can substitute the main language or give an empty block. Capture this behavior in the copy and don't assume the page is translated just because the buy button changed the caption.
Continue with: Hreflang: verify equivalent pages in four languages.
Check the addresses of one product
Each indexed language version must have a stable URL. The language switch preferably leads to the corresponding product, and not to the homepage. Check the direct opening of the URL in a new browser: the result should not depend only on the previous cookie. Canonical, internal links, and hreflang must describe one consistent URL strategy.
Continue with: OpenCart catalog imports: SKUs, options and validation.
Follow the full path of the order
Change the language in the category, on the product and after adding to the cart. Check options, amount, shipping and message language. If the language also changes the currency, test the rounding and final payment. Define a separate publishing policy for untranslated products, instead of creating a large number of identical language pages.
Is automatic translation of descriptions enough?
No. You need to check the terms, characteristics, units of measurement, option texts and the actual behavior of language URLs.