Change logic of i18n instance initializer
Change logic of i18n instance initializer

See #566

- Don't use the locales list to validate locale config/translation files
- Require at least a locale config and make translations optional

bastimeyer/livestreamer-twitch-gui,streamlink/streamlink-twitch-gui,bastimeyer/livestreamer-twitch-gui,streamlink/streamlink-twitch-gui,chhe/livestreamer-twitch-gui,chhe/livestreamer-twitch-gui,streamlink/streamlink-twitch-gui,chhe/livestreamer-twitch-gui,bastimeyer/livestreamer-twitch-gui