Localization: plural forms are not translated properly

[chrisrosset]

The current UI always displays certain labels in their plural forms:

Location	Example
Sidebar	1 segments
Sidebar	1 days
Sidebar	1 miles
Banner	1 flights
Banner	1 days
Banner	1 miles
Settings	Viewed 1 times

This is already wrong in English but fixing it properly for all languages (especially Lithuanian, Polish, and Russian) requires a switch to ngettext and enhancing our messages files.

https://www.gnu.org/software/gettext/manual/html_node/Plural-forms.html