Language course: which of the following is easiest to learn and understand? French, Italian, German, Spanish?

Based on your background, Spanish should be easiest to learn and understand since the Tagalog language has some Spanish influence so you may find some words similar. Moreover, in terms of relevance, Pre American literature in the Philippines are written in Spanish. Spanish is also the most spoken language in the world among your choices, and the third among all of the languages. So when it comes to learning another culture, you can get around more with Spanish.