I’m not a native speaker. Is that a problem?
No. The course is open to non-native speakers and around the world an ever increasing number of non-native speakers become CELTA-qualified each year. No formal academic requirements are set, but you must demonstrate in your application and in your interview that you have sufficient competence in both spoken and written English to cope with the demands of the course and the needs of your prospective students. In practice, this means you need a near-native-speaker competence, but it will be no barrier to you if you have acquired your present competence in the language through living in a native-speaker country, for example, without taking any examinations. It’s also worth remembering that as someone who has almost certainly studied the language formally yourself at some point, you will actually have an advantage over native speakers in some areas such as grammar knowledge and you will probably also be more sensitive to your students’ needs.