In which language or languages were your sacred texts originally written? Is it important that these writings be translated into modern languages or should the texts be read in the original language?

The Old Testament was written in Hebrew, with a few passages in Aramaic. The New Testament was written in Koine Greek, the common Greek of the first century.
The scriptures in their original writing were directly inspired (breathed-out) by God, are without error, and are the highest and final authority in all matters of religion, and it is necessary that God’s people read, study, and know the Bible. It is obvious, however, that not everyone can read Greek and Hebrew, therefore, as the Westminster Confession of Faith rightly says, “the Scriptures are to be translated into the common language of every nation to which they come.”
For those who would serve as pastors and preachers in churches or train others in the scriptures it is critical that they be able to work in the original languages, so as not to need to blindly rely on the writings of others.