feat(i18n): add the Slovak (sk-SK) panel locale (#6889)

Adds a complete Slovak translation of every panel and bot string, registers
sk-SK in the language picker (a browser set to sk now lands on it instead of
English) and loads Ant Design's Slovak locale. The locale count in the READMEs,
docs and contributor guides moves from 13 to 14.

frontend/src/utils/index.ts

@@ -901,6 +901,7 @@ export class LanguageManager {
     { name: 'Український', value: 'uk-UA', icon: '🇺🇦' },
     { name: 'Türkçe', value: 'tr-TR', icon: '🇹🇷' },
     { name: 'Português', value: 'pt-BR', icon: '🇧🇷' },
+    { name: 'Slovenčina', value: 'sk-SK', icon: '🇸🇰' },
   ];
 
   static getLanguage(scope: LanguageScope = 'panel'): string {
@@ -931,6 +932,7 @@ export class LanguageManager {
         ['uk', LanguageManager.supportedLanguages[10].value],
         ['tr', LanguageManager.supportedLanguages[11].value],
         ['pt', LanguageManager.supportedLanguages[12].value],
+        ['sk', LanguageManager.supportedLanguages[13].value],
       ];
 
       simularLangs.forEach((pair) => {