Localization files are in Localization/CODE.lproj/Localizable.strings
e.g.
Localization/es-419/Localizable.strings
Localization/fr/Localizable.strings
The format is:
The string found in the code (English)
=
The string to localize to
;
e.g.:
"Yes" = "Oui";
If you copy the English translation and fill in translations, and want to see if a file has any non-translated items
Run this to find all the strings that are the same on both sides of the equals sign:
cut -f1 -d\= Localizable.strings > first && cut -f2 -d\= Localizable.strings | sed 's/.$//' > last && diff -wy first last | grep -v \| && rm first last
This may give some false positives, e.g. in French, "Photo" and "Date" are the same in English and French.