Translation:The flowers that we arranged for Teachers' Day have come.
This one was very hard, because at first it's not clear how much of the first half of the sentence is attached to the participle. To work it out, I had to realize that either of the plural nouns could be the subject. Usually the first one is the subject, but here, it was part of a clause. No question, just commenting.
Oh, I believe you on that! I've already had the experience of saying "with this much study, surely I can read a few lines in _" and finding that I can't even begin to piece together the meaning. I see that both gerunds and -DIk- are the problem.
Want to toss out one reason why Öğretmenler is clearly ruled out as the subject? Now that I understand the sentence, I can see that it's part of a compound word, Teachers Day, but since usually a noun at the beginning does turn out to be the subject, I can't see any marker that should have flagged it as ruled out of hand.
The first marker for me was that if "Öğretmenler" was the subject, then "günü için" would have to mean something on its own. I could not work out a reason why "gün" was accusative or possessed, so I gave it back "Öğretmenler" to turn it into a compound noun.
The other thing I saw was that "çiçekler" was right next to the verb, and plural, but not cased, which made me suspicious that it could not be a direct or indirect object of "geldi."
@MimiB_Velo : Your comment came across humorously to me because of your explanation for "arrange" and "arrange for". I'm sure my English is good enough to explain that "arranged" means to have placed in a certain order or (loosely) to have made a plan. "Arranged for" means that instructions were given for something to happen. In this case the instructions, i.e. orders, were given ( to someone) "to deliver" flowers. "To deliver" is an assumption because once the flowers came (delivered), the given sentence was created to report that an order was arranged (planned) and its consequence is the reported delivery. Sorry for the long-winded explanation.
I think so because of the Turkish word "geldi" Geldi is past tense, so is "came". BUT "have come" is "present perfect" tense. So now, although 'have come" may be an acceptable translation to some, if it were me translating, I would translate "geldi" to "came" and not "have come". BUT that is me. :)