Nationals of EU countries, Switzerland, Norway and Iceland may work freely in Spain, and hence, Mallorca. Virtually everyone else needs to obtain, from a Spanish consulate in their country of residence, a work permit and (for stays of more than 90 days) a residence visa.
Many bars (especially of the UK and Irish persuasion), restaurants and other businesses are run by foreigners and look for temporary staff in summer. Check any local press in foreign languages, which carry ads for waiters, nannies, chefs, babysitters, cleaners and the like.
Translating and interpreting could be an option if you are fluent both in Spanish and a language in demand. You can start a job search on the web, for instance at Think Spain (www.thinkspain.com).