Find all msgstr which are either not empty or multilines using regexp in a po file

In a .po file, what regexp could I use to find out all msgstr lines being either

msgstr "some text"

or which spread on several lines:

msgstr ""
"some multiline text"
"goes here"

but not empty ones:

msgstr ""

?

For the moment I'm using this:

(msgstr "[\D\s]+")|(msgstr ""[\n\D\s]+")

But it's not fully working.

If all following lines should start with a double quote with at least a single character:

^msgstr (?:"[^"\r\n]+"|.*(?:\n"[^\r\n"]+")+)

The pattern matches:

• ^ Start of string
• msgstr Match literally
• (?: Non capture group for 2 alternatives
  • "[^"\r\n]+" Match from an opening till closing double quote with at least one character other than a double quote or newline
  • | Or
  • .* Match the whole line
  • (?:\n"[^\r\n"]+")+ Repeat matching 1 or more lines with at least one character other than a double quote or newline
• )Close the non capture group

Regex demo

If the following lines can also be empty:

^msgstr (?:"[^"\r\n]+"|.*(?:\n".*")+)

Regex demo