It depends on the religion. The holy book of Christianity, the Bible, was originally written in Hebrew, Aramaic, and Greek. The holy book of Islam, the Quran, is in Arabic. Hinduism has multiple holy texts written in Sanskrit. Buddhism's primary text, the Tripitaka, was written in Pali.
It is written in (and identical with) the Tanakh (Hebrew Bible).
World's Religions by Huston Smith is not extensive, but it is well done.
The Tanakh (Hebrew Bible) is in Hebrew (almost all of the chapters. A few chapters are in Aramaic).
If you are talking about the Hebrew Bible, it represents the Jewish people (although other religions such as Christianity also consider it to be holy).
The Hebrew holy books are collectively called Tanakh (×ª× ×´×š)
because that's the language it was originally written in. (Only Christians choose to read the Bible in translation. Jews prefer the original Hebrew.)
There are several - different religions have different holy books.
The holy book of Judaism is the Torah, which includes the first five books of the Hebrew Bible. The holy book of Christianity is the Bible, which includes the Old Testament and the New Testament. The holy book of Islam is the Quran, believed to be the word of God as revealed to the Prophet Muhammad.
Almost all major religions have holy books and holy languages.
The Christian Bible is the most sold book in the world.
The Bible is the holy book for Jews (Old Testament) and Christians (New Testament) and the Koran is the holy book for Muslims.