What is the Singular/Plural for Karma?

Question

If datum is the singular for data, is karmum the singular for karma?

Is premium the singular for premia?

Or, is karma the singular and karmae the plural?

I know it is originally a Sanskrit word. But since it has been adopted into the English Language we must supply English grammatical structure to allow for effective communication.

So, if we needed plural for the word karma, should it be

Karmas or

Karmae or

should we declare karma a collective noun or

should we have karma plural and karmum singular?

Answer 1

Karma is the singular and plural of itself, which is similar to deer, fish and sheep.  

Answer 2

Although it's commonly used in many languages, 'karma' is not an English word. It is Hindi or Sanskrit and is an abstract idea: fate.

Foreign words used in English often don't have equivalent plural forms.

-um and -a, and -a and -ae are used for Latin- or Greek-derived words.

Does 'karma' have a plural form in the original language?

"...we must supply English grammatical structure to allow for effective communication."

Don't you think 'karma' is perfectly acceptable and you're just being pedantic?