Should I Learn Arabic or Islamic Studies?

I would advise the following:

Learn the basics that you must know of your Islamic beliefs, the basic rules of acts of worship and transactions that you need, and the basic Islamic etiquettes and morals in your native tongue. This does not require too much study.

After that, put your heart, time, and efforts in learning and mastering the classical Arabic language from qualified teachers.

First you would need to go through a curriculum designed for non-Arabs, until you reach an advanced level where you can read and listen with a comprehension of 90% or more.

Then, once you have graduated from that program, you can start excelling in vocabulary, grammar, morphology, eloquence, literature and poetry the way an Arab student would study.

At the same time, you can start learning the sciences of the religion hand-in-hand with your Arabic studies, if you wish to be a serious student of knowledge.

A program based on:
- memorization, understanding and mastery of theory and application.
- taking it step by step (beginner, intermediate, advanced,...)
- comprehensive and well rounded program that includes all sciences.

Here is an excellent website that lays out a framework for students of knowledge to tread the path of Islamic scholarship.

takw.in

As for those who wish to read advanced topics in Islam through English translations, this goes against the way of the scholars of the past, keeps a student handicapped, and causes many problems.

Even if a person does not wish to become specialized in the Islamic sciences and does not want to become a student of the Islamic sciences, he will still benefit TREMENDOUSLY from learning Arabic and taking Islamic knowledge from the original sources. It's a great achievement to be able to understand the Quran, Tafsir, Hadeeth, etc. in the original classical Arabic, and the difference between hearing/reading the original vs. the translation is like the difference between night and day.

And Allah knows best.