Hi.
Preferences > Tweaks > "Set the list of words considered to be "articles" for sort strings" uses the following default expression:
title_sort_articles = '^(A|The|An)\s+'
This is very useful for the English language titles.
But, because I gather both English language books and French language books in my library, I have to extend the expression, if I want to get a correct title sort for the French language books.
So,
though I know strictly nothing as a programmer 
, I tried to extend the expression as following:
title_sort_articles = "^(A|The|An|Un|Une|L'|Le|La|Les|Des)\\s+"
I used " at the beginning and at the end of the expression, instead of ', because ' is used in the definite article L'.
This includes (links to en.wiktionary.org):
If
it matches well for un, une, des, le, la, les, the expression doesn't match for the only definite article “
l'”, which is, before a vowel (beginning the first adjective or the first noun in the book title, in my library) and
without any space, an apocoristic form of “le” and “la”.
So I think that my expression is not the right one, because of this “space problem”, and I would really enjoy to know how I could write it to allow a right title sort for someting as:
- “L'ultime secret” (article + adjective + noun),
- or “L'arbre des possibles” (article + noun + other),
titles which are not sorted, now, and stay the same in 'Title sort' zone of the 'Book details' window.