Nomenclature of simple molecules
In English, French and German, the names are less systematic. Here are some examples from English:

\begin{array}{|c|c|c|} 
\hline
\text{Formula} &amp;  \text{Name} &amp; \text{Oxidation #}  \\
\hline
\ce{FeCl2 }&amp; \text{ferrous chloride, iron(II) chloride} &amp;  +2\\
\hline
\ce{FeCl3 }&amp; \text{ferric chloride, iron (III) chloride} &amp;  +3\\
\hline
\ce{N2O}&amp; \text{nitrous oxide} &amp;  +1 \\
\hline
\ce{NO}&amp; \text{nitric oxide} &amp;  +2\\
\hline
\ce{HNO2}&amp; \text{nitrous acid} &amp;  +3\\
\hline
\ce{HNO3}&amp; \text{nitric acid} &amp;  +5\\
\hline
\ce{NO2-}&amp; \text{nitrite} &amp;  +3\\
\hline
\ce{NO3-}&amp; \text{nitrate} &amp;  +5\\
\hline
\ce{N^3-}&amp; \text{nitride} &amp;  -3\\
\hline
\ce{CrO}&amp; \text{chromous oxide} &amp;  +2\\
\hline
\ce{CrO3}&amp; \text{chromic oxide, chromium trioxide} &amp;  +6\\
\hline
\ce{Cr2O3}&amp; \text{chromium (III) oxide} &amp;  +3\\
\hline
\ce{H2CrO4}&amp; \text{chromic acid} &amp;  +6\\
\hline
\ce{HCl}&amp; \text{hydrochloric acid} &amp;  -1\\
\hline
\ce{HClO}&amp; \text{hypochlorous acid} &amp;  +1\\
\hline
\ce{HClO2}&amp; \text{chlorous acid} &amp;  +3\\
\hline
\ce{HClO3}&amp; \text{chloric acid} &amp;  +5\\
\hline
\ce{HClO4}&amp; \text{perchloric acid} &amp;  +7\\
\hline
\ce{Al2O3}&amp; \text{aluminum oxide} &amp;  +3\\
\hline
\ce{CaO}&amp; \text{calcium oxide} &amp;  +2\\
\hline
\ce{Li2O}&amp; \text{lithium oxide} &amp;  +1\\
\hline
\end{array}

I think this is what happens if names of substances were chosen before the concept of oxidation state (and electrons etc) existed. It would be nice to have something more systematic, but that would mess up all the older literature.

It would be fascinating (to me, at least) to see the Slovak names in another column of this table. Also, I am glad that chemical formulae exist that are universal in any language.