#MediaWiki uses the language names as defined in the CLDR. It is therefore important that people compile a list of the translations for their language make them available to be used as the standard translation.
Arno did exactly that. The list he created contains all the codes as used for Wikipedia combined with the translation in Esperanto. It is an important effort and it would be great when we have such a list for all the other Wikipedia languages as well.
As standards are standards, we were asked to provide the list in an XML format. It took some pastes and find and replaces and it looks good. The only problem is that some of the codes used are not standard codes. Several codes have been removed, "als" for instance is the code for Albanian Tosk not Alleman. There may be some other "language codes" in there that are not recognised in a standard.
When your language can do with additional translations, please follow the Esperanto example and provide a list of translations in your language.