July 28 (Reuters) - Language learning app Duolingo Inc’s shares rose nearly 39% in their U.S. market debut on Wednesday, giving it a valuation of $6.5 billion on a fully-diluted basis. The company’s stock opened at $141.4 per share, blowing past the initial public offering price of $102 per share. Reporting by Niket Nishant in Bengaluru; Editing by Devika Syamnath Our Standards: The Thomson Reuters Trust Principles.