Set RSS feed language

Hi all,
i’m having problems setting up my blog’s feed language.

The only error i get is

column 12: language must be an ISO-639 language code:

Now, the problem is that the language tag is empty

...
<lastBuildDate>Mon, 25 Aug 2014 09:14:50 +0000</lastBuildDate>
<language></language>
<sy:updatePeriod>hourly</sy:updatePeriod>
<sy:updateFrequency>1</sy:updateFrequency>
...

I want to set a value there, but i’m not quite sure how to do it?

Is there a better option than editing my theme’s functions.php file like this:

<?php
add_action('init','fix_rss');
function fix__rss(){
		update_option('rss_language','en');
}
?>

I’m not sure if this is the correct method mostly because i don’t know what caused the reset of the language value, so if i remove that bit of code from the functions.php file, it can be reset again? And if i leave it – i don’t know if i’m wasting resources without a reason.