A page like <https://launchpad.net/distros/ubuntu/dapper/+source/skim/+pots/desktop/ru/+translate> has a "Make suggestions from:" menu with 560 languages in it. This is much greater than the number of languages Launchpad lets you translate, because the suggestions sometimes come from translations with rare or synonymous language codes that were imported from elsewhere.
But many of these languages are very similar, if not identical, to each other, and there is little if any reason to want to see suggestions from just *one* of them. For example, if translating into Chinese (Taiwan), you don't want to see suggestions just from Chinese (zh), or just from Chinese (China) (zh_CN), or just from Chinese (Hong Kong) (zh_HK), or just from Chinese (Singapore) (zh_SG); you want to see suggestions from all four at once. The same applies to the various varieties of Spanish, the varieties of Tigrinya, maybe the varieties of Arabic, and so on.
Launchpad should know that these language varieties are related, and aggregate them for the purpose of showing suggestions.
A similar thing can be said for the dialects of English, like en_GB, en_AU, en_ZA, en_IN and so on. I work on both en_GB and en_AU translations, and I would like to see how things may be worded in other variants as well.