The Arabic language of letters, sounds, words, sentences, terms, literacy, and all aspects of the language, has never undergone a change in the course of history. It is recorded in the book Jami’ul Bayan fi Tafsiril Qur’an by Imam At-Tabari and Ad-Durar Al-Mantsur by Imam Ibnu Asakir that Adam as the first man to be Arabic when he was in heaven as told by Al-Quran letter of Al-Baqarah 35-37 and the language recorded in the Quran is still the same language we use today. Although there are popular Arabic languages (‘ammiyyah) different from the Arabic Quran (Fusha), the use of the’ ammiyyah ‘does not shift the position of Arabic Fusha as the real Arabic and does not change the Arabic identity which remains awake as the awareness of the Qur’an guaranteed by Allah SWT (Al-Hijr: 9). In the meantime, you can go to http://www.arabic.world/learn-arabic-online to learn Arabic online.
While other languages such as English have changed the vocabulary and the terms according to the changing times. English is originally an Anglo Frisian tribal dialect of Western German origin brought by German invaders to British soil. Then the Scandinavian colonization of the 8th and 9th centuries AD and the Norwegians in the 11th century changed radically the vocabulary and grammatical of English. English literature in the 5th century AD is very different from the English literature written in the 12th century AD because of the change in word order and terms. Then it changed again in the 15th century AD and 17 AD to become the English we use today.