Poland

The Polish language is one of the most difficult languages in the world.

An excerpt from the article 31 facts about Poland
The grammar of Polish is very complicated. There are five different parts of speech: a verb, a noun, an adjective, a numeral word and a pronoun. There are also diacritical letters: ą, ć, ę, ł, ń, ó, ś, ź, ż. All this sometimes makes foreigners who are trying to master Polish language overwhelmed.