"文字出现以前的" can be translated into English as "pre-literacy" or "before the advent of writing."
"Pre-literacy" is a more technical or academic term that refers to the period or state before the development of writing systems.
"Before the advent of writing" is a more descriptive phrase that clearly conveys the meaning of being prior to the emergence of written language.
Both expressions are appropriate depending on the context and the level of formality required.