what's the antecedent of population? which or whom?
On our planet, the total population is 6,914 million, among which the number of people speaking English, Chinese, Spanish, Hindi, French, Arabic, Russian, Portuegese, German, Japanese and Korean combined altogether is 5,474 million.

and does this sentence have any other problems to you?I would appreciate if you suggest a more native expression of this sentence.

Question

what's the antecedent of population? which or whom?
On our planet, the total population is 6,914 million, among which the number of people speaking English, Chinese, Spanish, Hindi, French, Arabic, Russian, Portuegese, German, Japanese and Korean combined altogether is 5,474 million. 

and does this sentence have any other problems to you?I would appreciate if you suggest a more native expression of this sentence.

Answer

If I were writing this myself, I would say:

There are 6.9 billion people on Earth, 5.4 billion of whom speak either English, Chinese, Spanish, Hindi, French, Arabic, Russian, Portuegese, German, Japanese or Korean.

Answer

On our planet, the total population is 6,914 million, among which the number of people speaking English, Chinese, Spanish, Hindi, French, Arabic, Russian, Portuguese, German, Japanese OR Korean, combined together, is 5,474 million.

Apart from the OR and a comma, everything is fine.

You can use which or whom for population.