I have several themes that contain .mo and .po files for translations.
The only reference to these files in the code is similar to this:
load_theme_textdomain('ThemeName',$template_dir.'/lang');
Would it be safe to delete the lang directory from these themes if I don't need to translate the theme for any reason? There are language files for English (en_US), but it doesn't look like they are actually used by the themes since the text is directly in the PHP files...
Sorry if this is a dumb question, I'm just not really sure how these files work with WordPress.
In your code you will see commands like
__('Some text','Themename');
_e('Some text','Themename');
If you set WP_LANG to "de_DE" in case you are in Germany, your WordPress installation will look for the file Themename-de_DE.mo in the /lang folder to find a translation.
If you remove the files/folder I would also remove the load_theme_textdomain('ThemeName',$template_dir.'/lang'); command. The files can all be removed but as mentioned in the comments, they will return on update.