Add new i18n languages and update existent ones

- Add 21 new languages where the UI was translated (all translations
  are 100% complete except for Chinese Simplified (96%)
  and Amharic (37%)).
- Update some translations for preexistent languages.

Change-Id: I64be0a2dd551c12af1547a616b4f49f97c471bde
diff --git a/src/_locales/en/messages.json b/src/_locales/en/messages.json
index 1595e38..3ba9d52 100644
--- a/src/_locales/en/messages.json
+++ b/src/_locales/en/messages.json
@@ -54,7 +54,7 @@
 		"description": "Option which defines how should the app behave in relation to tabs."
 	},
 	"options_tabsoption_3": {
-		"message": "Open Google Translate in a panel and override the last translation (need to activate <a href='chrome://flags/#enable-panels' id='panelsflag'>--enable-panels</a> flag). <sup style='color:red; font-weight: bold;'>EXPERIMENTAL</sup>",
+		"message": "Open Google Translate in a panel (you need to activate <a href='chrome://flags/#enable-panels' id='panelsflag'>--enable-panels</a> flag). <sup style='color:red; font-weight: bold;'> EXPERIMENTAL</sup>",
 		"description": "Option which defines how should the app behave in relation to tabs."
 	},
 	"options_savebutton": {