Formal:
* J'aime toutes les matières. (I like all subjects.) - This is the most literal translation, but it sounds a bit stiff.
* Je suis passionné(e) par toutes les matières. (I am passionate about all subjects.) - This is a stronger expression and emphasizes your enthusiasm.
Informal:
* J'adore toutes les matières! (I love all subjects!) - This is more informal and expresses strong liking.
* Je trouve toutes les matières intéressantes. (I find all subjects interesting.) - This is a more nuanced way of expressing your interest.
Specific Situations:
* Je suis bon(ne) dans toutes les matières. (I am good at all subjects.) - If you want to emphasize your abilities.
* J'apprends facilement toutes les matières. (I learn easily all subjects.) - If you want to highlight your learning ability.
Ultimately, the best way to say "I love all subjects" in French depends on the situation and the desired tone.