Comment # 2 on bug 1192290 from Lukas Ocilka

How this works: When a language is switched in YaST, it also calls libzypp and
tries to select all packages that provide translations for all installed
packages that match the new language. But YaST doesn't do it package by
package, it tells libzypp to do it all at once.

The problem is when some package
a.) does not have translations at all
b.) does not provide them in a way that allow for auto-selection

As an example, check "Provides" / "Supplements" in those packages that were
installed. For me, this is e.g., yast2-trans-cs (one package per language):

Provides:
locale(yast2:cs)
yast2-trans-cs = 84.87.20210502.7b34dbceae-1.1

Supplements:
(yast2 and namespace:language(cs))

Or MozillaThunderbird-translations-common (one package for many translations):

Provides:
locale(MozillaThunderbird:ar;ca;cs;da;de;el;en_GB;es_AR;es_CL;es_ES;fi;fr;hu;it;ja;ko;nb_NO;nl;pl;pt_BR;pt_PT;ru;sv_SE;zh_CN;zh_TW)
MozillaThunderbird-translations-common = 78.13.0-8.36.1
MozillaThunderbird-translations-common(x86-64) = 78.13.0-8.36.1

Supplements:
(MozillaThunderbird and (namespace:language(ar) or namespace:language(ca) or
namespace:language(cs) or namespace:language(da) or namespace:language(de) or
namespace:language(el) or namespace:language(en_GB) or
namespace:language(es_AR) or namespace:language(es_CL) or
namespace:language(es_ES) or namespace:language(fi) or namespace:language(fr)
or namespace:language(hu) or namespace:language(it) or namespace:language(ja)
or namespace:language(ko) or namespace:language(nb_NO) or
namespace:language(nl) or namespace:language(pl) or namespace:language(pt_BR)
or namespace:language(pt_PT) or namespace:language(ru) or
namespace:language(sv_SE) or namespace:language(zh_CN) or
namespace:language(zh_TW)))