Ques: নিত্যানন্দ - नित्यानन्द
Same letters, different script.
Technically it's Sanskrit, but the Devanagari alphabet is also used in Hindi.
The name Nitai, like Nimai, Gadai, Jagai, Balai etc. is Bengali, it is a short (affectionate) form, like Sammy or Bobby.
Answer by Shrila Nitaipreshthji:
A name is written as it is in any language. The name of a person does not change in any language. And Nitai is His eternal name in the Nitya-Lila, even though one may argue that it is a Bengali name. Bengali is the eternal language spoken in Goloka according to Shrila
Bhaktisiddhanta Sarasvati. Thus it does not matter whether Nitai is a Bengali or Sanskrit name, because it is His original name in Goloka, and because it is written in Devanagari as निताइ. There is no other way to write it in Devanagari or Sanskrit. Nitai Nam remains as "Nitai" when it is written in Devanagari. "Nityananda" is a different name and is written differently in Devanagari. There is no basis to say that in Devanagari or Sanskrit, Nitai cannot be addressed by Nitai Nam, but only can be addressed by Nityananda Nam, just because one may think that Nitai is a Bengali name. Again a name of a person is the same in all languages.
Shrila Narottam das Thakur clearly tells everyone to approach specifically the name of "Nitai" not "Nityananda", in his song verse: Nitai na bolilo mukhe, majilo sansar sukhe. So Nitai Nam is equally powerful and recommended as Nityananda Nam if not more.