At this period in history (commonly referred to as the 'Reformation' or 'Pre-Reformation') , the only church that existed was what is now called the Roman Catholic church.
During the time, the church services and the entire Bible were all in Latin. Anything for the educated class, such as treatises and official documents, were in Latin as well. Of course, few people actually spoke Latin, and this became a problem for the soon-to-be reformers (like Hus, Wycliffe, and Luther) who believed that the Bible was to be read by poor and rich alike, in the vernacular, meaning the language of the people. The translation of the Bible in the common language is also called the Protestant Bible.
The church forbade people to read the Bible because of many reasons. First, it meant that the people would find the faults in the church by comparing the church teachings to the Bible's teachings. These faults included the selling of indulgences, which increased the church's bank account. Obviously, the church officials disapproved of that. Second, the church officials believed that this would degrade God's word and that it could only be God's Holy, infallible word if it was in it's original language. Add the two reasons together and you can see that the church did not want the people reading the Bible for themselves.