From what I can gather about this set, the state of the alien dialog subs is interestingly inconsistent.
I, II, and IV have forced sub tracks.
VI and VII have burned in subs.
(IIRC, the others have no such subs).
To further clarify, subbed scenes have seamless branching. Both clean and burned in versions are on the discs. The variability was based on who reported it rather than the movies.