Multiple localization fixes

With the extractor PR, fixes title & description shown in the wrong language.
Fixed views / spectators counts possibly in the wrong language
Fixed live spectators not showing full count on detail page
Fixed LIVE shown on players, it shows translated instead

Fixed Videos string in search / three dots not available in Weblate
(because it was videos, but there already was a plural string named videos, in Weblate)

Subscriber count is always giving the short count.
We can't get exact number since this YouTube update: https://support.google.com/youtube/thread/6543166
But only short count (B, M, k), so showing full number, eg for 1.9M: 1,900,000, is wrong because the number could be 1,923,490 or 1,897,789…

Added a « sytem default » option to content language and country language selector.
It's the one selected by default (not en-GB anymore then), and correspond to the
language of the system / country of the system
By system I mean phone, tablet, TV…

Fixed russian showing - before time ago (eg 19hrs ago)
This is a workaround fix, I opened an issue on prettytime library repo.

Fixed russian plurals:
other was used instead of many for videos and subscribers

Fixed seek_duration english only

app/src/main/res/values-eo/strings.xml

@@ -537,4 +537,6 @@
     <string name="clear_download_history">Forviŝi la historion de elŝutoj</string>
     <string name="delete_downloaded_files">Forviŝi elŝutitajn dosierojn</string>
     <string name="deleted_downloads">%1$s elŝutoj forviŝitaj</string>
+    <string name="videos_string">Filmetoj</string>
+    <string name="dynamic_seek_duration_description">%s sekundoj</string>
 </resources>