I just tested Responsive 1.9.3 + Polylang 1.0.4 and confirm the problem. It comes from the suppression of the line 29 in front-page.php
$responsive_options = responsive_get_options();
$responsive_options is global, it seems logical not to reload it but it is most probably loaded before Polylang sets the language and so not filtered by Polylang. WPML sets the language sooner and thus is not affected by this change.
Which hook is used to set the language ?
WPML -> 'plugins_loaded', priority 1
Polylang, when setting the language from URL -> 'setup_theme', priority 5
Polylang, when setting the language from content -> 'wp', priority 5
For future, I plan to modify 'setup_theme', 5 to 'plugins_loaded', 1 when the language is set from url. It will improve the compatibility with some plugins and themes which also load strings very soon.
But for the other option, I am stuck to a late hook.
So for best compatibility, the strings should not be loaded before the 'wp' hook has been fired.