Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
When playing some content on Apple TV+ app, some language subtitles are not available such as Simplified Chinese, Japanese and Korean. However this is not the case, when same content is playing on iOS, MacOS, and Apple TV, these language subtitles are available.
Does this mean Roku does not support these language subtitles due to character code limitation? A similar case like opening a Word document without these languages installed on the OS it will show unreadable code.
For more information about that channel's features and functionality, you'll want to contact the channel provider support directly to inquire further. Many channels on Roku are developed and maintained by the channel provider themselves.