How would you translate the expression "by the way" into Italian? I think it can be translated as "a proposito", but I don't know if there are other possible translations.
As always, there is not a single translation that always fits. A proposito is often appropriate; depending on the register, also incidentalmente, the already-mentioned fra l'altro, or a periphrasis like dimenticavo, or già che ci siamo and so on.
[Added from a comment of mine:] To confirm that certain uses of “by the way” map perfectly on a proposito, let me point out that, while the original meaning of a proposito is something like “about the above, as regards what we said”, it is now used more generally to coordinate a not necessarily connected sentence. It is meaningful that Treccani for a proposito and the Oxford Dictionary of English in my computer for “by the way” give quite similar examples:
a p., dimenticavo di dirti che è arrivata una lettera per te
oh, by the way, while you were away I had a message.
By the way can be used in many context. As some have correctly identified, Fra l'altro is a correct translation. Another equivalent is Comunque or ad ogni modo which can also obtain a different meaning (literally, comunque means anyway, and so does ad ogni modo). In Italian, the three of them can all be used as a translation for by the way:
- By the way, I told him not to worry. - Comunque/Ad ogni modo, gli ho detto di non preoccuparsi.
- Let's talk about Francesco who, by the way, is her husband. - Parliamo di Francesco che, tra l'altro/comunque, è suo marito.
A proposito can still be used in the second case, but is a rather awkward translation for the expression by the way.
It's difficult to analyse this without more context, but ”By the way, I told him not to worry", might be something we'd say if referring back to an earlier subject or conversation or if saying something that indirectly related to the current subject, but you could also hear "in any case/anyway I told him not to worry", with the latter having an element of closure in it for a subject. I think the former is better translated by a proposito, while the latter would be better translated by comunque/ad ogni modo
For me the correct translation is:
But, for example, WordReference translate it in:
I think that
by the way have a one to many relation with Italian dictionary.