On Windows and macOS, we supply the Hunspell dictionaries along with Sigil. So they of course follow the start with language code naming convention.
Even MySpell, the predecessor to HunSpell, and ispell the predecessor to MySpell, all follow that naming convention of starting with a language code.
So there is a long long history on unix/linux for naming dictionaries so no one has to guess what language they are for especially as these dictionaries are shared across many apps.
That is why there really is no need to have to associate language codes with dictionaries. It would just make them harder to use and share with repeated mappings needed for multiple apps.
Sorry but Sigil will not be changing how we handle this.
Glad to hear you got it working!