Can a non-Buddhist get Nirvana? No religion teaches what Buddhism teaches at its core. A true Hindu or Christian or Muslim believes in God and soul.

Can a Hindu or a Christian or a Muslim, who is not aware of Buddhist philosophy, get Nirvana? 

If yes, how? Otherwise, why doesn't everyone become a Buddhist to attain supreme bliss?
Can a non-Buddhist get Nirvana?

Buddhism, Hinduism, Islam etc. are just words, conventional language. What is important is the teaching and practice of the teaching.
In the famous Maha-parinibbana Sutta, there is a passage where the Buddha explains to the wandering ascetic Subhadda, that &quot;in any doctrine &amp; discipline&quot;, that does not contain the Noble Eightfold Path, enlightened beings cannot be found.
It shows that only teachings that contain the Noble Eightfold Path can lead to freedom from suffering, to Nibbana.
The quoted passage can be found below.

Then Subhadda went to the Blessed One and exchanged courteous greetings with him. After an exchange of friendly greetings &amp; courtesies, he sat to one side. As he was sitting there, he said to the Blessed One, &quot;Venerable sir, these brahmans &amp; contemplatives, each with his group, each with his community, each the teacher of his group, an honored leader, well-regarded by people at large — i.e., Purana Kassapa, Makkhali Gosala, Ajita Kesakambalin, Pakudha Kaccayana, Sañjaya Belatthaputta, &amp; the Nigantha Nataputta: Do they all have direct knowledge as they themselves claim, or do they all not have direct knowledge, or do some of them have direct knowledge and some of them not?&quot;
&quot;Enough, Subhadda. Put this question aside. I will teach you the Dhamma. Listen, and pay close attention. I will speak.&quot;
&quot;Yes, lord,&quot; Subhadda answered, and the Blessed One said, &quot;In any doctrine &amp; discipline where the noble eightfold path is not found, no contemplative of the first... second... third... fourth order [stream-winner, once-returner, non-returner, or arahant] is found. But in any doctrine &amp; discipline where the noble eightfold path is found, contemplatives of the first... second... third... fourth order are found. The noble eightfold path is found in this doctrine &amp; discipline, and right here there are contemplatives of the first... second... third... fourth order. Other teachings are empty of knowledgeable contemplatives. And if the monks dwell rightly, this world will not be empty of arahants.&quot;