If you are using a specific release (like RUNE) and the language isn't switching:
Here’s the official list (from the Steam page) — all are available via RUNE language packs: horizon zero dawn remastered language packrune install
You can keep your system language as English but play with Japanese audio (or vice versa) by going to Settings > System > Language > Game Language (if available for this title) or by changing the Console Language temporarily just to trigger the download. If you are using a specific release (like
Why? Because shipping all 15+ language packs would double the download size (an extra 10–15 GB). Hence, . horizon zero dawn remastered language packrune install
If you have a standalone release and need to change the language manually without a launcher: