dunya tatlisi bitanem.

My try:

dünya = world

tatlýsý = the sweet

bitanem = my one and only

tatlýsý bitanem = my sweet one and only

its totally wrong henry.i guess "bitanem" could be translated  "my number one" in english. remember word by word is not an exact translation.

From TC online dictionary

bitanem my one and only; my only one

my unique one.....not necessarily the only one

Why is it totally wrong?

I assume bitanem originally came from "bir tane" with the ´m´ suffix for ´my´.

So the literal translation would therefore be "my one piece/item/single thing" which is very close to "my one and only". The dictionary here, and other translations seem to agree.

I include word for word translations sometimes, as often the translation requests are shortened pieces of text, and often out of context, so the meanings may vary considerably.

Also I thought in this request ´dünya´ did not show a relationship to the other words.

the world´s sweetest, my one and only.

 It does originate from that, but ´bitanem´ as a whole, nowadays is used as a term of endearment, meaning, as you said ´my one and only´ / ´my unique one´.

dünya tatlýsý belongs together. It is a connection with a compound marker, compare:

school = okul

bag = çanta

schoolbag = okul çantasý, the suffix shows us the connection between the two, making it ´schoolbag´.

dünya = world

tatlý = sweet

dünya tatlýsý= the world´s sweetest, again the connection is shown by the -sý- suffix.

We also have the Turkish version of ´miss world´ this way:

dünya güzeli = the worlds most beautiful.

Thanks for the explanation Deli_kizin.

I assumed that ´dünya´ needed the possessive ending

´dünyanýn tatlýsý´ to make it become ´the world´s sweetest´. 

 You are right actually.

the world´s sweetest would be ´dünyanýn (en) tatlýsý´.

But in Turkish we come across many examples that are build up like okul çantasý and that convey about the same meaning, just like the example of ´dünya güzeli´ I gave, which is the Turkish way of saying ´Miss World´.

Thanks again for the clarification. 

Local knowledge is always superior to dictionaries and guesswork!

 Yes, it definitely is! When I am not sure of a certain usage, I either ask, google, but generally prefer not to use it at all for example ´köylü güzeli´ can mean very diffirent things, a pretty girl in the village, but also in turkish cinema a wild, unmannered provincial girl who comes to the city and is taught etiquette, so you could well offend someone if you use it wrong

Whether rightly or wrongly,since I have been a member of TC ´bitanem´ has usually, to my recollection, been translated thus by both English and Turkish speakers.