PHP Errorwhen changing language

Hey there

I'm having a problem with changing the language of a WordPress-Site. 

Here's the error I get when I try to switch from english to german:
Warning: An unexpected error occurred. Something may be wrong with WordPress.org or this server’s configuration. If you continue to have problems, please try the support forums. (WordPress could not establish a secure connection to WordPress.org. Please contact your server administrator.) in /url/wp-admin/includes/translation-install.php on line 59

And here's what it say's in the file on line 59:

if ( $ssl && is_wp_error( $request ) ) {
trigger_error( __( ‘An unexpected error occurred. Something may be wrong with WordPress.org or this server’s configuration. If you continue to have problems, please try the support forums.’ ) . ‘ ‘ . __( ‘(WordPress could not establish a secure connection to WordPress.org. Please contact your server administrator.)’ ), headers_sent() || WP_DEBUG ? E_USER_WARNING : E_USER_NOTICE );

$request = wp_remote_post( $http_url, $options );
}`

Is it possible I get this error, because it’s a SFTP connection? What can I do to solve this?

Thanks in advance