In theory teachers need to have the proper diploma (for example Master degree in teaching) validated by the Education Council.

The Education Council in the UAE says that in general a teacher must have a bachelor degree with some teaching qualification and teaching experience (at least 2 years). However other degrees can also be accepted when the experience is greater (they can also accept TEFL, depending on experience).

PS: You don't need to learn the local language if you are teaching in a national or international school in English but of course it is appreciated to know a little bit.

Information is available: http://www.moe.gov.ae/english/Pages/default.aspx