Reader: send user's language to improve search results

[nheagy]

The reader search appears to use geolocation of user IPs to guess appropriate the language to use for results. Instead, the app can supply the users current locale or language setting to get the appropriate results.

[igotdes]

A user has submitted a similar request in #5987836-zen:

Create language filters, I don't speak Chinese nor Italian or Spanish, recommended blogs' feed doesn't make sense, I can't use it because I want to choose only blogs in portuguese language to appear on my feed.