I happened to have read your advertisement and have decided to apply for the job. The following is my self-introduction.
As a high school student， having been learning English for many years， I have a good command of English， especially spoken English. Warm-hearted and outgoing， I am always willing to help others. In addition， by taking exercise every day， I am in good condition. Therefore， I am convinced that I’m equal to this job.
By acting as a translator for you， unpaid as it is， not only will it enrich my life， but also be of great benefit to me in the long run. Apart from gaining the opportunity to practise my spoken English， I can accumulate some valuable job experience.
I’d appreciate it if you could take my application into consideration. Looking forward to your early reply！