The 4.4.0.beta2 with Slovenian language pack on OSX shows the locale in the About window, but for Slovenian as locale string "sl_" is shown, which either means that "sl_SI" was meant to be displayed so the string got truncated or "sl" was meant to be seen, so it should be truncated more?
Probably this should be tested with other locales and their identifiers of different length.
This is interesting. In LO Version: 184.108.40.206.alpha0+
Build ID: a26222f5af55e8ffe9784dd411485d3c5c72e983
TinderBox: MacOSX-x86_64@49-TDF, Branch:master, Time: 2014-12-07_00:14:47
I do see "de_" but this is the nightly "as is" no language pack installed. So maybe this is the region? However your point persists and is valid.
I can confirm that with 4.4.2 RC2 on OS X I see only "sl_", whereas the same Windows version shows "sl_SI", so it seems OS related bug, as reported.
It seems to be corrected with LO50RC4, now it writes:
So I am closing this as WORKSFORME.
This got fixed with http://cgit.freedesktop.org/libreoffice/core/commit/?id=f318e305b6afa715ef759b8589823da53b812a88 since April.