Professional word taster James Harbeck shows you how to identify different languages by identifying the unique characters they use.
Ř, ř: This is the classic distinctive Czech letter. It stands for a sound so difficult to learn, even Czech kids take years to get it right. Another character that only Czech has is Ů/ů. (Does that have a familiar ring? Don't conf it with å — see below.)
Ł, ł: If you see this letter (as in Łódź, and standing for a sound like "w"), you are very likely looking at Polish. For further confirmation, look for Ż/ż. (Polish also has many other accented characters, including ź — not the same as ż — but some other languages have these, too).