この英文なのですが... what is the function of なのですが?

Question:

Here is the original question:
No one could understand why he killed himself. It just didn`t make sense.
この英文なのですが、前半は「彼がなぜ自殺したのかは誰もわからない」でいいので…

この英文 = this English sentence

if なの　and が　are omitted, the sentence becomes この英文です, which translates to "It is an English sentence"

now if が　is added, then it becomes この英文ですが。。。 I still can't fully understand the use of が at the end of a sentence. One thing I know is that が in this case can be translated to "but" or "and".

as for なの, I'm completely clueless about its use. :/

Answer:

この英文なのですが This is the english text, but...

なのですが means the same as ..ですが (...is but...). The difference is that なの makes the sentence more formal and by using it is like you are more sure about what you're saying. But it is known as a feminine way to talk. Most guys say なん instead of なの.

For example: How old are you?
Formal: 何歳ですか
Most formal: 何歳なのですか
Feminine: 何歳なの?
Masculine - Formal (I often use this): 何歳なん?