normally i say turkce´de nasil soyleyebilirsin?

Today i have seen another way...turkce´de nasil denir? Is this also correct?

Yes it is correct. It is a passive sentence and means "How is it said in Turkish?"

yardimin icin tesekkur ederim.

Some more examples:

Demek=to say

Denmek=to be said

Söylemek=to talk

Söylenmek=to be told

Türkçe+de----------------------->Türkçede (in Turkish) [TDK is not separating the inflectional suffixes after the language names. Therefore I show it in that way like I have been doing while I write lesson too. Otherwise, the inflectional suffixes are absolutely separated when they are brought to the proper nouns.]

For example, they haven´t separated the inflectional suffix of "Almanca" even if they had separated the inflectional of "Türkiye" in that example sentence.

http://tdk.gov.tr/index.php?option=com_bts&arama=kelime&guid=TDK.GTS.52e0d43e721e63.51126740

Almanca+a(dative)--------------->Almancaya (to German)

Türkiye´deyken epeyce çalışmıştım Almancaya. (I have studied German very much when I was in Turkey.)

the best syntax: Türkiye´deyken Almancaya epeyce çalışmıştım.

demek (to say)

de+n(passive)+r(present simple)---->denir (it is said)

Türkçede nasıl denir? (How do people express it in Turkish? (direct: How is it said/expressed in Turkish?))

http://www.turkishclass.com/turkish_lesson_337

Evet, ikisi de doğru. (Yes, both are correct.)