This is the 3938th most frequent Arabic word.
بالعربية
"In Arabic."
The word 'بالعربية' indicates the language in which the activities (reading and writing) are performed, i.e., Arabic.
أنا أحب القراءة والكتابة بالعربية.
I love reading and writing in Arabic.
Here 'بالعربية' conveys that the study materials or subject are in the Arabic language.
درست القواعد والمفردات بالعربية.
I studied grammar and vocabulary in Arabic.
In this case, 'بالعربية' signifies the medium of communication being Arabic.