Unisubs GH-915 - Update iso language code for somali

This patch changes the ISO code of Somalian language from "som" to "so", as "so" is the
ISO 639-1 standard.

This patch needs special attention with testing. As discussed with @bendk, we have some information on the database that depends on that code. Our doubt is if the information gets updated with this patch since it regenerates a list of internal languages and another list of Amara's languages.