A group of refugees from the Gamma Quadrant claims that Bajor is the homeland they've long been searching for.
One of the recurring themes for the original Star Trek series is that because something is different or unattractive, it doesn't mean it's wrong or unworthy. A recurring theme for The Next Generation is, "How can we help this group of people who are struggling with a problem?" "Sanctuary" combines the two ideas into an immigration-themed episode that plays out as an average Deep Space Nine filler story.
The episode begins with a Star Trek faux pas: it attempts to explain how the universal translator works. The problem is that the past (and future) precedents for communication between aliens on Star Trek can't be rationally and consistently explained and simply have to be accepted an artistic liberty. As such, it's in the show's best interest to mention the universal translator in abstract terms and not call attention to its details. This episode, however, tries to be cute by having aliens we have trouble understanding. \The DS9 writers have since admitted that this is just a stall tactic because the real story is too short for a full episode. The idea works in TNG's fifth season episode "Darmok" because that episode avoids the specifics of the technology. In contradistinction, "Sanctuary" awkwardly discusses it and raises more questions than it answers. How does the universal translator immediately and identify translate the languages of other aliens we haven't encountered before? Why do the lip movements always look like English? Heck, in the TNG episode "First Contact", Riker spends the episode seemingly speaking English with a race of aliens who don't know he's not one of them. Did the . project the foreign words in his own voice and project a holographic mouth making the sounds? But I digress.
The story itself, once the communication issue is buried, moves along nicely and is enjoyable. It's especially a hoot to see William Schallert "Nilz Baris" in the original series episode "The Trouble With Tribbles" as a Bajoran musician who opens the episode with a rendition of the Deep Space Nine theme. Ultimately, however, "Sanctuary" sidesteps offering a clear statement on the immigration issue, playing both sides of the fence and probably pleasing no one in the process.