Implement Polish translation (#6283)

* Initial polish translation sweep

* rewrite feeds page flavor text

* bring up to date with dev branch, revisit some strings

* redoing some more...

* bring up to date

* rm dead strings, try out a different phrasing for threaded mode str

prev translation was nonsensical - we're already calling threads "wątki". let's try "recursive tree" instead to describe what threaded mode does

* tweaks here and there

* more tweaks. sign translation file

TL note: trying a new space-saving translation for send via direct message, old one made the context menu stretch

* space-saving translations for profile tabs

* up to date

* tl latest changes

* some small fixes

* few more tweaks around profile editing strings

* i dislike gendered languages

* yet more tweaks

* Update dates.ts

* Review suggestions (1)

* tiny fixes

* Review suggestions (2)

* Review suggestions (3)

* Review suggestions (4)

* "Anuluj wyciszenie"

* A few new strings

* Remove dead strings again

* Review suggestions (5)

* te -> to

---------

Co-authored-by: Frudrax Cheng <i@cynosura.one>

lingui.config.js

@@ -15,6 +15,7 @@ module.exports = {
     'it',
     'ja',
     'ko',
+    'pl',
     'pt-BR',
     'ru',
     'th',