This book contains a lot of rare words.

Learning Dalmatian language is difficult.

He fell into a deep sleep and was muttering in his sleep.

He was sleeping while sleeptalking.

This new word is a portmanteau, combining two words.

He is studying every day to learn the local language.

He is attending university to learn the Tocharian language.

When you use a negation, the meaning of the sentence is reversed.

My friend is studying Portuguese.

There are many polysemous words in Japanese.