Movies that have multiple language audio tracks available in youtube, when playing on roku tv with surround sound 5.1 option chosen, English audio track becomes unavailable, doesn't appear in list. Multiple people are reporting this issue.
When in youtube mobile app on android no such issue seems to be there as surround sound option not available.
It's not clear what you're saying, but this would be Youtube's issue, not Roku's. Roku devices do have limited support for the multitude of audio codecs, so that may have something to do with it.