Why learning sanskrit is important

Sanskrit has all the knowledge - 

1. Vedas 

2. Puraanas 

3. Ithihaasas 

4. Upanishads 

5. Brahma sutra

6. All Dharshanas

7. Bhagavad Gita

8. Sthotras

9. Subhashithams etc

Also its grammar is so complete that learning any other language in the world will be easy. 

Sanskrit has the power to cure diseases. 

Among the Dharma, Artha, Kaama and Moksha, you can find a lot of materials in other languages including Tamil for the first three. But for moksha you need to know sanskrit, because of the above resources. 

Even though there are translated documents available, there is no guarantee that they are correct. 

My experience 

I did my MA project in skanda purana. While doing it, I understood that

1. Tamil skanda purana is different from the sanskrit one.

2. Tamil focuses on surasamharam only but sanskrit focuses on all shivalayas

3. There is no proper English translation available in the world

So learning with the original is better. The language of values is sanskrit.