Check translation contracts offline, add Swedish to the installer and enable the website languages

- Offline checks for terminal and website catalogs reject translations that change commands, paths, identifiers or placeholders
- Terminal and documentation texts that broke those contracts are corrected in every language
- Swedish can be chosen in the stable and beta installers
- The website routes, language switcher and exported pages cover the eight languages, with the shared website texts in each of them
- Website documentation translations are generated only when requested
- From PR #475 by @jcastro

web/messages/en/common.json

@@ -28,7 +28,12 @@
     "switcher": "Language",
     "en": "English",
     "es": "Español",
-    "sk": "Slovenčina"
+    "sk": "Slovenčina",
+    "de": "Deutsch",
+    "fr": "Français",
+    "it": "Italiano",
+    "pt": "Português",
+    "sv": "Svenska"
   },
   "resources": {
     "documentation": {