grammar 問題

文法上和句式有少少問題，那些連接和因果關係斷開了。
依你的原句用詞，應該寫成：

Because we are Chinese, naturally learning Putonghua must be easier (這裏不用,) when comparing to learning English, in which Chinese is our mother language.

雖然複雜地表達，但有點style.

第二句就冇style了。
Because we are Chinese, Chinese is our mother tongue. Naturally, learning Putonghua is easier when comparing to English.

Because..., ....是一個相連關係。必須要停full stop。Naturally...是另一個引出的主題或論述，要再開新一句。不要以為思想/構思上一連串的關係便, ..., ..., ...下去的。句法上是一組組的，然後每組句子之間的關係要由讀者連上，否則寫一篇文便只有一個"."

As /being a Chinese, it is easier for us to learn Putonghua than English since Chinese is our mother tongue.

英文用字是沒有錯, 但部份表達太主觀 ( must ) ! 並且 >

這段的英文表達是廣東話的口語化直釋的.

以下的修改, 表達也許會較好 :

To compare learning english and chinese, Putonghua should
be easier than english because Putonghua is similar to chinese,
also which is our mother tongue.

有....
我會咁講:
It is easier for us to learn Putonghua than English because we are Chinese. Our mother language is Cantonese which is also written Chinese as same as Putonghua.