Use the supported mobile download route
Rakuten’s current UK help describes downloads in compatible Android and iOS apps, explicitly excluding Android TV from that Android download support. A film visible in a television library is therefore not evidence that the television can create the same offline copy. Inspect the wanted film or episode for its Download button on the actual mobile device.
Choose the offered language before downloading
The publisher describes a language-choice window after Download is pressed. Read that choice before starting a long transfer, especially when two viewers need different audio. The film’s ordinary detail page also lists its available audio and subtitle options. Use those item-level details rather than assuming that changing an account preference supplies every language for every title.
Wait for completion rather than only a library entry
Rakuten shows circular progress while a download is underway. Its offline instructions require the transfer to be complete before relying on playback without data. The app stores downloaded material in its library area; simply seeing a purchased title in the library is a different observation from confirming that its device copy finished downloading.
Reopen without a connection before departure
The help specifically instructs closing the app after a successful download and reopening it without internet, using airplane mode. In that state it opens the Downloads folder and shows downloaded content. Test this on the intended device while there is still time to correct an incomplete transfer. Rakuten also specifies internal device memory, so unused space on a removable card is not automatically space available for this download route.
Questions, answered
Does Rakuten’s Android download guidance include Android TV?
No. The cited offline help explicitly excludes it.
Does a title in the library prove its download is complete?
No. Check the download progress and the offline Downloads view.