There is no vocative case in Japanese.

Kakuro is my best friend.

He passed the book to me.

This is an old Japanese textbook that explains the usage of '變格' in detail.

I'm sorry, but I don't speak Japanese.

I am studying for the Japanese Language Proficiency Test next year.

He said, 'Haste makes waste,' and proceeded with his work without rushing.

He is attending a programming school to learn object-oriented languages.

Natural language processing is a technology that allows computers to understand and analyze human language.

He is an expert in comparative linguistics.