On my system, app-dicts/myspell-en is pulled in by app-text/hunspell with LINGUAS="en_US en", as one would expect. However, this one myspell language installs the Australian, UK, US, Canadian, New Zealand, and South African (as well as the OED English) dictionaries, of which only one is useful to me and, presumably, virtually all users who are native speakers of an English national variant. Now, according to the Gentoo wiki (specifically, https://wiki.gentoo.org/wiki/Localization/HOWTO#LINGUAS) it is possible to place specific locales in LINGUAS, yet these locales are not honored by the broken-down myspell packages. Since the package behavior deviates from the configuration in a situation where the details would appear to matter, I think this qualifies as a bug. Ideally, each actual locale would have its own myspell ebuild. This has a practical effect due to an unfortunate Firefox behavior where the alphabetically first dictionary installed is selected for its default spellcheck dictionary, as described in the linked URL, but this is not a reason to consider the ebuild setup a bug; it's just how I learned of it. For reasons of correctness, this is already wrong. Reproducible: Always
This is the way it is done for app-dicts/myspell-pt{,-br} and -de{,-alt} and probably other locales. Sounds like an improvement.
The myspell-es package doesn't do this (and there are many, many more locales in it). I will take this into consideration.
Sorry for the noise; I think the correct fix might actually to respect regional LINGUAS settings in myspell-en. I'll need feedback from other devs before I proceed on this however. This could benefit other packages like myspell-es.
I've already committed changes to myspell-en that make it l10n use flag compliant, that should take care of this issue as I understand it. If i'm mistaken, please re-open