"Who is the strange suit for?"
Translation:Pro koho je ten zvláštní oblek?
I'm trying to understand when I need to include "ten" etc and when I can leave it out. There was another example in which zvláštní or maybe poslední was used and considered specific enough that adding "ten" wasn't required to account for the English "the" (and I think counted wrong when I added ten to the sentence but I can't remember for sure).
Is there a reason this sentence in particular needs ten?
To a large degree you just have to get a feel for that. Like the learners of English for the English tenses. There are no simple rules for either, I am afraid. I still make frequent mistakes in English tenses and you should be prepared for the same with Czech demonstratives.
The most basic explanation is:
Is there some unique suite that can be regarded as (the) "zvláštní oblek". Are people engaged in the conversation likely to call one of the suits (the) "zvláštní oblek"? Here it seems very unlikely. If I have one cow in at home and it is sick and I say "Krávě není dobře." to my wife, we both know that "kráva" is the only cow we have and we mean that one and we may commonly call about it that way. Bot not a strange suit. Yes, if I have one red suit and we frequently discuss it than "červený oblek" (the suit known as the red suit) can probably also sometimes mean "the red suit" but it is still more likely to speak about a "ten červený oblek", the suit that is red.