Some subtitle tracks strip out the Na'vi subtitles because they are technically "forced" subtitles. Look for a file specifically labeled or "Foreign Parts Only" when downloading. This track will only show subtitles when Na'vi is spoken.
Now, go enjoy the crystal-clear dialogue of Pandora.
: Offers a wide range of English subtitle files specifically synced for different releases, such as 1080p WEB-DL or 720p BluRay.