Two reasons:
Before v1.5, language files were stored in .archive files. After v1.5, CDPR introduced a new sound bank system to support PS5 and Xbox Series X|S spatial audio. Consequently, using a v1.31 language pack on a v1.5 game will cause: cyberpunk 2077 language pack v1 5codex verified
(If you want, I can list exact filenames to look for inside a typical v1.5 language pack or provide step-by-step file paths for Windows/Steam installs.) Report: Cyberpunk 2077 — Language Pack v1
Installation and Compatibility
Download this free language pack to add Chinese (Simplified) voiceovers to Cyberpunk 2077: Ultimate Edition on Nintendo Switch™ 2. Steam and Games - Language Settings Title: Cyberpunk 2077 — Language Pack v1