There are two Polish localizations available in Orion:
polski - Polish
polski (Polska) - Polish (Poland)
yet when I switch to the second one and reboot, Orion still uses first one.

Theoretically, Orion should switch to the second version of Polish but there is just one variant of this language so it does not make sense to have both of them listed. The name of the language should be "polski - Polish" but it should use translalted strings from "polski (Polska) - Polish (Poland)" as the second one is more complete. On Localazy , it's "Polish" and "Polish (Poland)", respectively. Translated strings should be copied from "Polish (Poland)" to "Polish", then "Polish (Poland)" should be removed.

0.99.134-beta
Sequoia (15)