Should I dual major in college?
If I want to be a high school teacher, would it be wise to dual major in math and a foreign language? Would it make schools more likely to hire me?
Do you enjoy math and a foreign language? If you enjoy both, then go for it. Otherwise, major in what you love. College Classes are not always fun and if you don't enjoy the subject, you will be tempted to skip class and/or not do the work outside of class. Don't worry about what career you will get outside class or how marketable you will be; instead focus on finding joy in your studies. If you enjoy your work, it will be infectious and anyone will want you to work for them.
My sister is a school teacher and she teaches in low-income/ poverty districts. If you have the drive to be a teacher, there are always openings in those school districts.