I have a system where only the English Language is installed
(/var/lib/zypp/RequestedLocales has en_US).

If I run the YaST package manager (qt or ncurses),
enable Ignore Recommended Packages for Already Installed Packages
(which will be the default, see
https://bugzilla.opensuse.org/show_bug.cgi?id=902394 )
and add another language (eg Czech), no additional packages are selected.

This is contrary to my expectation, since I consider Czech to be a new
"package" so its recommended dependencies such as desktop-translations and
bundle-lang-common-cs should be selected for installation.

It works if I disable the Ignore...Already option.

I wondered why the solver would behave so and I noticed that most language
dependencies were expressed as conjunctions, eg

bundle-lang-common-cs:
  Supplements: bash & namespace:language(cs)
  (it also has this, and I wonder why)
  Provides: locale (bash:cs)

so in one way I see that bash is "already installed" so there's a pretext for
not installing the bundle. OTOH the language is new, so the user expectation
is IMHO clear.

desktop-translations is even more interesting, since there is no conjunction,
OTOH there is a disjunction. (Why not simply list a Supplements for each?)
  Supplements: namespace:language(af) | ... | namespace:language(cs) | ...


I noticed all this when converting the Ignore...Already option to a one-time
command similar to `zypper inr`. Gabi then argued that it was necessary for
it to remain an option so that language rpms can be installed. I think that
they should obey the onlyRequires option, which is newly exposed in the UIs
as "Install Recommended Packages" (boo#900853).

Overall, I consider this a part of a bigger cleanup of Recommends,
https://fate.suse.com/318099