Standardization
We use the ISO 639-3 standard to classify languages. This standard is extremely extensive and meant to cover all known languages. In the case of Swahili for example, the ISO 639-1 code issw and the ISO 639-2 code is swa.
The ISO 639-3 standard allows for a more detailed classification of Swahili, using swc for Congo Swahili and swh for Coastal Swahili.