if you have an accusative object, you can place the subject after it to emphasize that it was THIS PERSON who made the action.
For example, if somebody asks "Who ate the sugar?" it would be very awkward to say "Ben şekeri yedim" or "şekeri yedim." You should say "Şekeri ben yedim."
En français, je peux traduire "sekeri ben yerim" par "moi, je mange le sucre" en english "I just love it" That insist on the emotion, the good sensation, strong feeling eating sugar. In french, i translate "ben sekeri yerim" by "yes i eat sugar" because eat sugar is commonplace.
No, it is not awkward at all to say "Ben şekeri yerim.", but it just has a slightly different meaning. As you say it is about the emphasis. If you say "Ben şekeri yerim." (which is the regular SOV order), the emphasis is on "şekeri". I think it is safe to say that in Turkish the component right before the verb is always the one with the strongest emphasis. If you want to put extra emphasis on the subject, you place it before the verb instead of its usual place (the beginning of the sentence).
Apparently "O portakalı yer" is the normal order but if you want to insist that it is 'he' as opposed to somebody else who is eating the orange, then the order is "Portakalı o yer". In the exercise above, "Şekeri ben yerim." has the word order "Şekeri" and "ben" reversed to insist that it is "I" and not someone else.
No, if the direct object is indefinite(has no accusative marker) you can't change the position of it. People would understand the meaning due to the '-im' suffix here(though it is still incorrect) but if the subject is third person this rule becomes more important.
Balık karınca yer: The fish eats ants/an ant.
Karınca balık yer: The ant eats fish/a fish.
I am not sure from which langauge you are talking about here, so I will talk about both.
"Şekerleri ben yerim" would mean "I eat the candies/sweets." If you want a plural specific direct object, you do have to use the plural suffix.
"sugar" cannot be in the plural in English. Also, because "şeker" is in the accusative case, you know it must be a singular direct object.
Gwynifer, the english sentence is "i eat THE sugar". In Turkish, "the sugar" is "şekeri", ("şeker"+"i" accusative suffix, with the transitive verb "yemek"> "yerim". As Ynotsnikwah explains clearly above . It is helpfull to read all the comments before asking. Ok? I do that since the beginning and i always find the answer i need.
"The sugar I ate" is not a complete sentence in English. It is a literal translation of the Turkish phrase, "Şekeri ben yerim". "The sugar" is the object, "I" is the subject which in this case is placed after the object and before the verb to stress that it is "I" who eats the sugar and not someone else. Turkish syntax (structure) is usually subject/object /verb whereas English syntax is subject/verb/object.
ynotsnikwak, do you know that site, about word order in Turkish: https://en.wikipedia.org/wiki/Turkish_grammar#Word_order? They explain how word order can change in different ways. Very clear and usefull.
Chernomorets, we use the accusative case when the object of the verb, here "the sugar" is definite and direct, with a transitive verb. "Yemek" is a transitive verb. We don't use the accusative case when the object is undefinite, unspecific,even with a transitive verb, as in "i eat sugar", any sugar. In this example: "i eat sugar when i'm tired". We don't know if it is brown sugar, white sugar...about the quantity, etc.