Language argument "lang=" doesn't seem to work with get_timelines

[mfuoli]

Problem

The language argument doesn't seem to work with the command get_timelines. When I specify English for the language filter, for example, I still get examples in other languages.

Expected behavior

Reproduce the problem

Below is an example of a simple query which retrieves tweets in English and Spanish, even though I specify English as the target language.

## insert code here
LATAM <- get_timelines("LATAMAirlines", n = 500, lang = "en") 

rtweet version

## copy/paste output
packageVersion("rtweet")

Session info

## copy/paste output
sessionInfo()

Token

## copy/paste output
rtweet::get_token()

[hadley]

I don't see any evidence that this is supported by the twitter API, so I think this is a case of #470.