أنا أتعلم العربية
العربي وصف مذكر لايصح لوصف اللغة ،اللغة مؤنثة إذا يكون الوصف تابعا للموصوف.
(العربي)
is a masculine adjective it won't fit for اللغة
because اللغة is a feminine noun
in Arabic the adjective must be modified to take the same gender of the noun , اللغة the language is logicaly known as feminine noun in Arabic
so here you have to add ة to العربي to make it feminine adjective too
you end up saying
أنا أتعلم العربية
or
أنا أتعلم اللغة العربية
in the first sentence we removed the object and just put the adjective it's possible.in the second we put both