Relax the tests of the listing of available languages.

Currently language list/language table is hard coded in tests which makes it unnecessarily hard to add new languages (see [comment-1](https://github.com/cucumber/gherkin/pull/296#issuecomment-35805164) and [comment-2](https://github.com/cucumber/gherkin/pull/290#issuecomment-35842201))

Therefore, to simplify the addition of new languages, remove the hard coded language list/language table in the tests. Instead test a sample of languages in addition to having the tests read the list of language codes from the file [i18n.json](https://github.com/cucumber/gherkin/blob/master/lib/gherkin/i18n.json)