qu’il dut qualifier auprès de sa femme de courtoise mais ferme et qui visait à chasser de l’existence commune ces relents plébéiens

This sentence has not been translated well.

M. de Broglie has a high responsability work, therefore, he has an image to keep and transmit. And also, he is a husband, and he want to keep his pride regarding his wife. So, he reported to his wife that the ‘intervention’ – the fact that he spoke with the concierge to make her stop cooking stinky dishes – was both courteous (to maintain his position image) but firm (to show that he is the boss, he is the man). The use of “il dut” refers to some kind of hypothesis. Renee supposed he reported the conversation to his wife in this way.

Then, Renee is on one side relieved than she doesn’t have to cook stinky dishes anymore (she did that to act like a stereotyped concierge) and on the other side, she act as she had no other choice because her “boss” – M. de Broglie – gave her an order. It is some kind of a false submission.

Français

Pour répondre à la sixième question : c’est un exercice littéraire pour francophone ; bien que la ponctuation soit correcte, il est possible d’augmenter la lisibilité en remplaçant les , par des – indiquant une incise et d’encadrer de parenthèses les phrases qui s’intercalent ou s’ajoutent :

Il m’était si humiliant de devoir cuisiner ces mets infâmes que (l’intervention de M. de Broglie[,|–] le conseiller d’État du premier [N.B. : étage, c’est une concierge qui parle, un des degré le plus bas de l’échelle sociale, elle ne parle pas politique pour ne pas se mettre les résidents à dos][,|–]) ((qu’il dut qualifier auprès de sa femme de courtoise mais ferme) et (qui visait à chasser de l’existence commune ces relents plébéiens)), fut un soulagement immense (que je dissimulai du mieux que je le pus sous l’apparence d’une obéissance contrainte).

Ce blog relève deux phrases, dont celle-ci, qui ont une construction complexe et qui ne sont pas à employer tous les jours. Elles peuvent être une solution pour exprimer deux points de vue opposés, tels cette concierge face à une société qui s’accommodent sur les apparences.

Un sous-découpage en phrases courtes – comme avec les () ci-dessus – rendrait la phrase technique, avec des redites pour rappeler après chaque point le sujet du discours.

Pour un traducteur, ces phrases peuvent surgir en littérature ou dans des formules réglementaires concernant des points intriqués, et sûrement dans d’autres textes ; utiliser un redécoupage plus fin jusqu’à ce que la lecture soit cohérente, chercher chaque mot qui pose problème en affinant perception du contexte sont les premiers outils, ensuite chacun est libre de rester proche du mot à mot ou d’essayer des transpositions.

_{Merci à cl-r pour sa contribution à cette réponse.}

English

General understanding of the sentence

Il m’était si humiliant de devoir cuisiner ces mets infâmes que l’intervention de M. de Broglie, le conseiller d’Etat du premier, qu‘il dut qualifier auprès de sa femme de courtoise mais ferme et qui visait à chasser de l’existence commune ces relents plébéiens, fut un soulagement immense que je dissimulai du mieux que je le pus sous l’apparence d’une obéissance contrainte.

The greatest difficulty here lies in identifying what the Councilor qualifies as “courteous but firm”.

Looking for excerpts of this book, it is quite easy to find the English version of this sentence (which will answer question 1):

It was so humiliating for me to have to cook such loathsome dishes that when Monsieur de Broglie — the State Councilor on the first floor — intervened, (an intervention he described to his wife as being “courteous but firm,” whose only intention was to rid our communal habitat of such plebeian effluvia), it came as an immense relief, one I concealed as best I could beneath an expression of reluctant compliance.

Is it correct French?

Yes, it is. It does not mean it is easy to understand, even for a native French like myself (I actually found it easier to understand the English version than the French one).

Why is that? Because the sentence is written want-to-be-elegant style, which ends up being so stilted you need more than one pass to attach each element. This can be immediately perceived with the length of the sentence (six conjugated verbs!).

This is actually a literary exercise for francophones; though the punctuation is correct, it could be made easier to read by replacing the commas , with dashes – to show interpolated clauses and use parenthese around other sentences that add up.

Il m’était si humiliant de devoir cuisiner ces mets infâmes que (l’intervention de M. de Broglie [,|–] le conseiller d’État du premier [N.B. : étage, c’est une concierge qui parle, un des degré le plus bas de l’échelle sociale, elle ne parle pas politique pour ne pas se mettre les résidents à dos][,| –]) ((qu’il dut qualifier auprès de sa femme de courtoise mais ferme) et (qui visait à chasser de l’existence commune ces relents plébéiens)), fut un soulagement immense (que je dissimulai du mieux que je le pus sous l’apparence d’une obéissance contrainte).

This blog highlights two sentences in the book which have a complex sentence and are not for everyday use. They can express opposite point of views, such as this janitor facing a society who agree on apparences.

A cut-out of the sentences in shorter ones – such as with the () above – would make the sentence technical, with repetitions to make it clear after each period which is the subject.

For translators, such sentences can happen in literature or in administrative formulaes concerning intricate subjects, and certainly in other texts; using a finer cut-out until the reading is clearer, looking for each word being a problem are the first tools. You can try word-by-word or transpose depending on the case and what suits you best.

Do you need to learn that?

Short answer: probably not.

You will rarely meet such complicated sentences. They work only in written form, because I think most people do need several readings before getting it OK. I am even surprised to find something so complicated:

• in a novel;
• in so recent a novel (2006).

I deem this style to rather be found in essays or older books.

As to expressing yourself, do not event think of something like that before being bilingual. The general advice I give to people expressing themselves in a foreign language is to keep things short and simple. Make more sentences, use only phrases you fully understand. In the end, it is better to be understood with elementary but clear sentences than to be misunderstood with style and phrasing.

Bonus: Use of devoir

About question 2, “il dut qualifier” could be translated “he had to describe” or “he likely described”. This is ambiguous and the English version does not shed any light on this, though Steven BENET‘s answer brings some context which might help understanding why the use of this verb.