"Je ne comprends que lorsque" is “ne” the “ne explétif” here?

Question

I'm trying to learn French by reading a French novel side by side (located here), and I think some of the translations are wrong but that's another conversation.

je me retrouve aussi novice et je ne comprends que lorsque vous m’avez une fois de plus développé votre procédé

The bold part is translated to "I only understand when"

I know the ne explétif is used to denote negative meanings. However online notes say it's usually after the verb, and I'm not understanding how this could be a negative meaning.

How is ne being used here? The way I read it now is "I do not understand then when", but that's obviously wrong.

As for the other conversation if you have any recommendations on books/websites that have this side by side translation, I'd truly appreciate any suggestions.

Answer 1

The

ne ... que

construct expresses a negative meaning in the same way that "nothing but" does in english.

For instance,

Je ne mange que des légumes

means "I eat nothing but vegetables"

Your example is a bit more subtle, but works in the same way:

Je ne comprends que lorsque...

becomes "I understand nothing, except when...", which in more common English would become "I only understand when"

In terms of the resources you were asking for, you may want to check this existing question

Answer 2

Incidentally, the same can be said for the following sentence:

Ce n'est que parce que je t'aime qu'il m'arrive parfois de me montrer dure avec toi.

=

It's only because I care about you that I might sometimes come across as harsh towards you.