fix(webui): support pl pluralization

Co-authored-by: @SubZeroPL

komga-webui/src/i18n.ts

@@ -3,7 +3,7 @@ import VueI18n, {LocaleMessages} from 'vue-i18n'
 
 Vue.use(VueI18n)
 
-function loadLocaleMessages (): LocaleMessages {
+function loadLocaleMessages(): LocaleMessages {
   const locales = require.context('./locales', true, /[A-Za-z0-9-_,\s]+\.json$/i)
   const messages: LocaleMessages = {}
   locales.keys().forEach(key => {
@@ -20,4 +20,34 @@ export default new VueI18n({
   locale: process.env.VUE_APP_I18N_LOCALE || 'en',
   fallbackLocale: process.env.VUE_APP_I18N_FALLBACK_LOCALE || 'en',
   messages: loadLocaleMessages(),
+  pluralizationRules: {
+    /**
+     * @param choice {number} a choice index given by the input to $tc: `$tc('path.to.rule', choiceIndex)`
+     * @param choicesLength {number} an overall amount of available choices
+     * @returns a final choice index to select plural word by
+     */
+    'pl': function (choice, choicesLength) {
+      // brak stron
+      if (choice === 0) {
+        return 0
+      }
+
+      // 1 strona
+      if (choice === 1) {
+        return 1
+      }
+
+      const betweenTwoAndFour = ((choice % 10) >= 2 && (choice % 10) <= 4)
+      const lessThanTen = choice < 10
+      const moreThanTwenty = choice > 20
+
+      // 2 strony, 3 strony, 4 strony, 22 strony ...
+      if (betweenTwoAndFour && (lessThanTen || moreThanTwenty)) {
+        return 2
+      }
+
+      // other cases, 5 stron, 67 stron, 259 stron and so on
+      return (choicesLength < 4) ? 2 : 3
+    },
+  },
 })