Non-core Namespaces should be translatable through Special:AdvancedTranslate[1] just as their Special Pages[2] and Magic Words[3] are already.
[1] https://translatewiki.net/w/i.php?language=sv&module=namespace&title=Special%3AAdvancedTranslate
[2] https://translatewiki.net/w/i.php?language=sv&module=special&title=Special%3AAdvancedTranslate
[3] https://translatewiki.net/w/i.php?language=sv&module=words&title=Special%3AAdvancedTranslate