Hi,
Sorry for the delay.
Please note that your question is not about HikaShop, it is about setting up your website menus in different languages, which is something you do in Joomla to link to pages where HikaShop cant hen display its content.
The issue is apparently with the way you translated your menu item. Normally, you should just have your menu item
plekochania.com/en/yarn/mirasol
and translate its name (an potentially its alias) with Falang so that when you switch the language, you're still on the same menu item but the text of the menu is in the new language.
As I don't know exactly how you configured your Joomla menus in your Joomla menu manager, I can't say for sure what is the problem, but if you just have one menu item with its translation handled by Falang, there is no reason that the content displayed when you click on the menu item link would be different with different languages. So please try that and that should solve the problem.
If that doesn't help, I'm still happy to help but I would really need to you post precise information of how you configured the menu items of your links (with screenshots of the options).