Don't pass `$this` by reference. Fixes #169.
Prevent continuous UPDATEs on admin screens.
The WPLANG constant is deprecated since WP 4.0. We now give preference to the WPLANG option when setting the defaults.
Implement `filemtime()` when enqueuing assets.
Avoid performing calculations on rewrite rule arrays on every page load.
Add the requested language code to the `bbl_lang_codes` filter.
Cache the value of `bbl_get_current_lang_code()` when registering post types.