"I am Japanese."
Go. 日本語 -> にほんご -> nihongo 語 means language. You can put go after many country names to mean their language. フランス語 -> フランスご -> furansugo -> French (language). English being a notable exception. England is イギリス -> igirisu But English is 英語 -> えいご -> eigo
I'm still learning so if I have anything wrong, please let me know.
日本 means Japan and 本 means book (or origin when combined with other characters). Japanese writing is a little confusing. Here's an introduction to Kanji (literally, Chinese character) http://www.guidetojapanese.org/learn/grammar/kanji