Final answer:
Archaeologists have been unable to translate Harappan language due to the lack of decodable material; as a result, significant aspects of the Indus valley civilization culture remain unknown.
Step-by-step explanation:
Archaeologists have not been able to translate the language of the Harappa artifacts because the script is still undeciphered. The writing system of the Indus valley civilization, comprising about four hundred phonogram signs, remains a mystery due to the absence of a bilingual inscription, such as the Rosetta Stone for Egyptian hieroglyphs, which could provide a direct comparison to known languages. Without a clear understanding of the language, crucial aspects of this ancient culture, including their political structures, beliefs, and daily life, elude modern scholarship. The intriguing layout of Harappa and Mohenjo-Daro suggests a certain level of urban planning and societal organization which, along with materials like cooking vessels and trade goods, offers some insight into their culture. However, major elements related to their literature, history, and legal systems can only be speculated upon until the script is deciphered.