As we all know, the plural of Jedi is Jedi.
In my country (Poland) the local title ("Ostatni Jedi") also uses words that have the same singular and plural form, so it's not conclusive. How is it in other countries?
Could it be that the title of the movie refers not to a single Last Jedi (Luke Skywalker), but maybe to more than one person? Maybe including Rey, maybe Yoda, maybe the whole concept of "time for the Jedi to end"?
As shown by existing answers, director Rian Johnson seems to have a clear answer to the question, but that doesn't make the title of his movie less ambiguous, especially since many of the film's official translations deviate from his opinion (neither do we know who was ultimately responsible for the title anyway). Of course the decisions of whatever international marketing division aren't necessarily more significant than the director's interpretation either, but this unclarity even among the official channels adds to the high ambiguity of the original title. Seeing how that ambiguity is just centred around the specificities of the English language and the declination of a fictitious word, it might be entirely coincidental and not intended by the film-makers at all, but it is still very much there, and quite apparently so (as your question and the interest it generates shows afterall).
We could argue if Luke Skywalker is the only Jedi left or if there are technically other Jedi around. But this is also made quite difficult by the unclarity what a "Jedi" actually is (which isn't helped by the institutionalized arm of the Jedi having been destroyed with the rise of the Empire at the end of the prequel trilogy, and the sequel trilogy bringing much more of the fuzzy mysticism back into the Jedi idea). Is it any force sensitive person? Is it some force sensitive gal carrying a bunch old Jedi codices around with her? Or is it only someone who went through a proper 4 year B.Sc. programme in Jedi?
But the ambiguity doesn't just end there. As other answers have shown, the films themselves do indeed use these words (in the title sequences as well as in dialogue) to describe a specific individual with them, Luke Skywalker that is. But then again, the mere fact that Luke might indeed be the last of the Jedi makes him also pretty much a representative of the very Jedi religion itself. So he might very well incorporate singular and plural in unison.
But beyond arguing about what a Jedi is, how many there are left, or what whoever from Disney thinks the title refers to, there is a strong theme of ending/renewing the era of the Jedi that drives itself through the movie. Afterall, Luke himself (at least initially) wants the Jedi to end for having grown arrogant and Kylo Ren actually agrees with him in that (as does Yoda to some degree). Although, the film isn't entirely uncompromising in its "out with the old one, in with the new one" attitude, especially when it has Rey save the old Jedi codices, there is a strong sense of, if not ending, then at least renewing or revising the Jedi idea. And you might argue that the notion of the entire Jedi era ending is represented more by the plural than by the singular, but that alone could very well just be a subjective impression, too.
What all these ramblings are hopefully showing is that this isn't really a simple question to answer. But it's also not a simple question to ask either, seeing how the ambiguity adds to the theme of ending the Jedi as well as, in its referral to Luke himself, to the question what Luke actually means for the Jedi as a whole and ultimately to the question what "Jedi" and being a Jedi really means, nothing of which is simple to answer. So even if that looks like a lame excuse, we might just resort to the platitude that the question itself is the answer. Coincidental or not, it's a really interesting question and Rian Johnson might either have been joking or a little bit too dismissive in his judgment of it. ;-)
Is the title “The Last Jedi” singular or plural?
During an interview with ABC News, director Rian Johnson said:
It's so funny when people started asking that, when the title was announced, because I never even pondered that question ... That seems like, to me, the most uninteresting question ... In my mind, it's singular.
If one's to consider the director's opinion as the de facto answer, well, then, there it is.
This is community-wiki, so please contribute!
Though Rian Johnson has stated the title is singular (as per Charles' answer), for the record, here's a list of international translations of The Last Jedi, categorized by whether they are singular, plural or indeterminate (such as in English or languages which do not have a singular/plural distinction at all). Titles with asterisks are taken from Wikipedia; those without are from the more official IMDB AKA page.
TO-DO:
Bosnia and Herzegovina (Bosnian title) Posljednji Jedi
Malayalam സ്റ്റാർ വാർസ് : ദ ലാസ്റ്റ് ജെഡൈ *
PLURAL
Farsi (Iran) آخرین جدای
Bulgaria Последните джедаи
Estonia Viimased jedid
France (& Canada) Les derniers Jedi
Hungary Az utolsó Jedik
Spanish-speaking countries Los últimos Jedi
Portuguese-speaking countries Os Últimos Jedi
French-speaking countries Les derniers Jedi
German-speaking countries Die letzten Jedi
Greece Οι τελευταίοι Τζεντάι
Italy Gli ultimi Jedi
Latvia Pēdējie Džedi *
Lithuania Paskutiniai Džedajai
Romania Ultimii Jedi
Russia Последние джедаи
Ukraine Останнi Джедаi
Serbia Poslednji džedaji
Israel אחרוני הג'דיי (Achroney haJedi)
Slovakia Poslední Jediovia
SINGULAR
Arabic الجيداي الأخير (Al-Jidai Al-Akheer)
Iceland Síðasti Jedinn *
India Aakhiri Yodha
Lithuania Paskutinis Džedajus [alternative] *
Croatia Poslednji Džedaj
Turkey Son Jedi
Georgia უკანასკნელი ჯედაი (Uk’anask’neli Jedai) *
Slovenia Poslednji jedi
INDETERMINATE
English (Original title) The last Jedi
Poland Ostatni Jedi
Japan 最後のジェダイ (Saigo no Jedai)
Korean 스타워즈: 라스트 제다이
Taiwan 最後的絕地武士 (Zuì hòu de Juédì Wǔshì) *
China 最后的绝地武士 (Zuì hòu de Juédì Wǔshì) *
Vietnam Jedi Cuối Cùng
Czech Republic Poslední z Jediů
Thai สตาร์ วอร์ส: ปัจฉิมบทแห่งเจได *
The title of the film is spoken twice in a conversation late in the movie.
Luke Skywalker: I failed you, Ben. I'm sorry.
Kylo Ren: I'm sure you are! The Resistance is dead, the war is over, and when I kill you, I will have killed the last Jedi!
Luke Skywalker: Amazing. Every word of what you just said was wrong. The Rebellion is reborn today. The war is just beginning. And I will not be the last Jedi.
At a stretch Kylo’s comment could be using “Jedi” as a plural, grouping in the students he killed prior to Episode VII, but Luke’s response only makes sense if the word is singular (though he denies that he is truly the last).
Luke Skywalker has vanished. In his absence, the sinister FIRST ORDER has risen from the ashes of the Empire and will not rest until Skywalker, the last Jedi, has been destroyed.
Although BEFORE the film was released Rian Johnson insisted it was singular and specifically pertained to Luke, which is also stated in The Force Awakens opening crawl, and in which Luke's initial beliefs in not wanting to train Rey, confirm his statements, I believe those ideas are contested by the film's end.
Although it took a bit of prodding, Luke does train Rey (also confirmed by action figures, Rey "Jedi Training"). So at the very least one can more safely say she became a Jedi apprentice. Now if she is truly a Jedi Knight by the film's end, I think is unclear, since he only gave her 3 lessons of the Jedi Order. However, she also has Jedi ancient texts, which may lead her to advance by the start of the next film.
It's true we have seen Force-Ghosts before, which have only ever been characters that were, at some point, Jedi. In this film however,(Jedi Master & Knight) Yoda's Force-Ghost not only appears, but seems to have evolved to near materialization. So there may be an argument to be had, if a Force Ghost of a Jedi (Master, Apprentice, Knight) appears, if it counts on as a "Jedi" on screen? But one may also point out that Force Ghosts can help train/teach, and even in some rare circumstances, interact with the corporeal world. Yoda's existence at the very least helps Luke, to help Rey, to help Leia & the resistance. Also one reason Force Ghosts can appear from the netherworld seems to rely on Jedi training, and thus so far, only Jedi have returned.
The film's ending scene. Although IMO the film's primary drive fixates on uncertainty, the ending with the young force-sensitive stable boy, Temiri Blagg, and tales of Luke Skywalker being passed on yet again, is like a song being sung across the galaxy. It's a symbol of hope--an awakening, suggesting that there may be more Jedi yet to come, although it is unclear if the new era of Jedi will resemble or embody the same exact principles or beliefs, as those seen in the recent past and if Rey is to be their new teacher.
Although he has turned to the dark side, Kylo Ren (Ben Solo) was also once a Jedi apprentice and the final film seems like much hangs on Rey saving him from the dark side and to see if he will finish going down the Jedi path.
But to fully answer the question is hard, because of where the boundaries really lie for what a Jedi is/can be, but if we only reduce the rank of Jedi within any given known order to "Master" or "Knight" and if we take everything that is not either fully corporeal in nature, currently on a Jedi path to Knighthood, or even Knighthood/Masters as a rank themselves, then it appears that Luke may have been the Last Jedi [KNIGHT/Master] in the film and by the films end, despite that others may be on their way and/or Ghosts of Jedi Knights/Masters can appear to help guide them.
It does not matter.
In either case, last refers to the ending of the Jedi class.
The same discussion about singular or plural has been with Return of the Jedi.
