R.- People who are learning Chinese are increasing.
No, people don't increase.
- The number of people who are learning Chinese is increasing.
Are both grammatically correct? Yes, but the first is not possible semantically.
Would it be OK to say "There are more people learning Chinese"?
No. To give your meaning, you'd have to say "There are more and more people learning Chinese"
Otherwise you need to specify 'more than what?' because you only have the first part of a comparison. You need a 'than' phrase.
"There are more people learning Chinese than Japanese"
"There are more people learning Chinese than there were a year ago"
"There are more people than cats learning Chinese"
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