"It doesn't matter where we have dinner; I'm really hungry."
Translation:Peu importe où nous dînons, j'ai vraiment faim.
This translates literally as "N'importe où nous dînons, j'ai vraiment faim.".
The problem is that the English sentence is not an accurate translation from the original French, which actually means "It matters little where we dine".
So the difference is:
- "Peu importe où …" → "It matters little where …"
- "N'importe où …" → "It doesn't matter where …" or "No matter where …"
- "N'importe que^ …" → "It doesn't matter what …" or "No matter what …"
However, I get the impression that a native speaker would tend to choose to use "Peu importe où …" at the beginning of the sentence and "n'importe où" within the body of the sentence.
Whereas "It matters little …" has gone out of fashion in English, and we would choose to say "It doesn't matter …" at the beginning of the sentence.
^ … or "n'importe quoi" within the body of the sentence.
And you don't consider your pidgin French sentence, with two clashing verbs in the initial clause, to be even more terrible?
What you are trying to say is "N'importe où on dîne", which should be accepted, even though I suspect that it is not what a native would choose to say.
It could be as simple as "or" ("ou") instead of "where" ("où"), or it could be that Duo is not accepting "N'importe où" at the beginning of the sentence because it wants you to learn and use "Peu importe".
Without more feedback on what variants have been accepted it is difficult to speculate.