"Licentiate in Interpreting" is what you're looking for. Licentiate is the term recommended by Nuffic (the Netherlands organization for international cooperation in higher education) in their glossary 'Nederlandse Hoger Onderwijs Termen in het Engels'.

Don't even start trying to compare it with a BA or MA, as you'll only end up tying yourself in knots, and its really for universities to decide what it might equivalate to in an international context. All your reader needs to know is that it is the degree awarded after completion of university studies in Belgium.

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Note added at 20 mins (2003-09-11 09:46:13 GMT) [[utf-8]]
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Many countries have credential evaluating bodies who can tell you what your foreign dilploma is worth in relation to degrees awarded in that country. This does not mean, however, that your licentiate degree will become a master\'s degree (or any other degree for that matter). Academic titles are usually protected, and the law of the country where the degree was obtained determines which title you may use. For example, in the Netherlands the law states that if you graduate with a \'doctorandus\' degree, you may use either the title \'doctorandus\' or MA/Msc. Whether this is correct/fair/honest or not is another matter....