|safety first |
सुरक्षा सर्वप्रथम (suraksha sarvapratham)
Yes, Hindi is the most prevalent language in India. It is spoken by roughly half the population of India, or about 500 million people. It is also widely understood in all the major cities in the non-Hindi speaking areas of the country like Calcutta, Mumbai, Hyderabad, Bangalore and Chennai. Also, the younger generation (school-attending) would all be familiar with Hindi as they learn it at school for about 10 years as a second language. Hindi is also the official language of India.
So your choice about Hindi as a representative language of India is without fault.
Coming to your other question, one possibility is:
सुरक्षा सर्वप्रथम (Suraksha Sarvapratham).
This means exactly Safety First. There is also the alliteration in the repetition of the S sound which makes the slogan more catchy and memorable.