Match the same content
The Ukrainian article should refer to its Russian, English and Czech versions, and not to the homepages of these languages. Check that each match is available and truly translated. If there is no translation, don't make up a URL for it and don't add it to the alternatives set.
Continue with: Multilingual OpenCart: catalog, URLs and language switching.
Check codes and reciprocity
For Ukrainian, the code uk is used, for Czech - cs. Each set page should contain links to itself and other available alternatives; check the backlinks. x-default may describe a fallback for users outside of the specified languages. All addresses must be complete and consistent with canonical.
Continue with: Sitemap maintenance: canonical URLs and accurate dates.
Check the HTML and sitemap
Language links can be described in ways supported by Google. If you use several, they must match. Check not just the source template, but the final HTML after caching and localization. Test the language switcher separately: it should preserve the context of the opened article or service.
Do I need to add a country to each language?
No. The region is indicated when the version is really intended for a particular market. Language and country are different characteristics, so combinations are chosen according to the content of the site.