Yes, translators cannot translate idioms. Clearly "Réveillé du pied gauche" is the French equivalent of the English expression "got out of the wrong side of bed", meaning started the day in a bad mood.
I learned French at school, then again in private tuition French lessons (No, not the kind of French lessons you see advertised in the phone kiosks outside Paddington station). And while this provided a good grounding (verbs and grammar) the only way to learn a language is to go to a country where they speak that language.
Otherwise, one sounds like an American gun nut who has Google-ised himself full of British gun control facts, and then purports to know what life is like in Britain. Translators cannot handle idioms (yet) just as Google cannot be used as a window on life in another country.