I find this translation misleading, because "May he use her restroom", as in "Is he allowed to use her restroom?" would be in German: "Darf er ihre Toilette benutzen?"
However, "Dürfte er ihre Toilette benutzen" would be equivalent in English to: "Would he be allowed to use her restroom?"
Dürfte is Konjunktiv 2, which means that it expresses an hypothetical situation, much like in English with the words "would" and "were", the only difference is that in German it is possible to use Konjunktiv 2 using only one word that has been "tempered" with, usually, but not exclusively, in the Präteritum form.
Er hat = he has. Er hatte = he had (past - Präteritum). Er hätte = he would have.
From this we can surmise that:
Er darf = he is allowed/he may. Er durfte= he was allowed (past - Präteritum). Er dürfte = he would be allowed.
Not a native speaker, but my understanding is dürfte is a conditional version of darf. It is tricky to translate them differently into English, but its like you're not asking if you're allowed to do something in the sense of it being against the rules, but rather just politely asking permission.
Surely for a simple request this ought to be 'darf er ihre Toilette benutzen?' 'Dürfte er ihre Toilette benutzen?' is Konjunktiv 2, i.e. conditional, and would mean 'Should he use her Toilet'? There must be a distinction in sense between a present indicative and a conditional, unless, despite the tense, this is just the way a German prefers to say it. Any native German speaker out there?!
as a child, i am expected to use 'may' because it is polite, therefore, it sounds completely normal to me. i assume that as you get older, you will use it less because one on the main places it is used is in school when talking to teachers, and at home when talking to your parents or guests.
You can't pretend that the UK is the entire world. If you are unwilling to learn English as it's used throughout the world, it makes me wonder why you would bother learning a foreign language. Most people in England are glad to know how English is used around the world.
If you don't like the way Americans use English, then don't forget that the land had many other languages that were spoken regularly until people came from Great Britain and refused to learn the language. English became the de facto language, and Americans noticed, as people came from and went to England, that the language was changing so fast over there that they predicted that within a few hundred years, the languages wouldn't be mutually intelligible. That didn't happen, but don't pretend that the language wasn't changing faster in England, or that the US wasn't retaining more traditional words. That's rubbish. (rubbish, by the way, is a newer word for garbage)