Wesleyan’s website only mentions recommendations from your teachers, so I don’t think an alumnus recommendation will add much unless that person is also your teacher in a core subject. I don’t think it would hurt either.
Wesleyan says that an interview is “highly recommended.” Have you scheduled an interview yet? December 11th is the last day to schedule one if you haven’t done this already. See: http://wesleyan.edu/admission/visiting_campus/interviews.html
I don’t think you need to leave anything out of your application. You might want to organize and package it a certain way though. Your art background is related to a major in Art History, so your artistic endeavors and achievements could be listed at or near the top of your activities/honors lists. Your language skills would be highly relevant to conducting research related to the Middle East and art history, so language studies and related cultural activities could also be featured high in your list of activities. Government is a component of Middle Eastern Studies, so your mock trial, UN and similar activities could be featured high on your activities list as well.
To make the best use of the space available, you may find that it helps to lump some activities together in the Activities section and give them labels that support your planned majors. For example, you could organize your activities under labels like these: Visual Arts (describe lessons, achievements and awards), Language Studies and Teaching (became fluent in English, Spanish, Arabic, Urdu, Hebrew, and taught Arabic locally and English in Pakistan), Political Science Clubs (Model UN, mock trial, constitutional debate, interfaith dialogues, etc.), Cultural Activities (dance - if relevant, other…), etc.
Your internship and legislative experience would go under Work Experience. Your volunteer activities would go under Volunteer Experience, and you could list your volunteering experiences in India and Nepal first to place more emphasis on them.
Good luck!