There are a number of differences between Czech and English when it comes to plural and countable nouns. We say watch, you say watches. You say hiccup, we say hiccups.
Another good example is the word dress. Šaty is plural in Czech but singular in English – and while Czech speakers usually use the word dress correctly, they often pair it with a plural verb.
For example, a Czech student might say, “I love your dress. They are lovely.” To an English person, this sounds confusing. How many dresses is this person talking about? One, two, all of them?
So, stick to the singular – “I love your dress. It is lovely.” – when you are talking about one dress. And use the plural when referring to more than one – “She always wears such nice dresses. They are beautiful.”