Add missing translation files and update translations

Files added:

```
new file:   plugins/poll/config/locales/client.ko.yml
new file:   plugins/poll/config/locales/client.pt.yml
new file:   plugins/poll/config/locales/client.ru.yml
new file:   plugins/poll/config/locales/server.ko.yml
new file:   plugins/poll/config/locales/server.pt.yml
new file:   plugins/poll/config/locales/server.ru.yml
new file:   public/403.es.html
new file:   public/403.ko.html
new file:   public/403.pt.html
new file:   public/422.es.html
new file:   public/422.ko.html
new file:   public/422.pt.html
new file:   public/500.es.html
new file:   public/500.ko.html
new file:   public/500.pt.html
new file:   public/503.es.html
new file:   public/503.ko.html
new file:   public/503.pt.html
new file:   vendor/gems/discourse_imgur/lib/discourse_imgur/locale/server.ko.yml
```

Tests are passing.

cc @nlalonde