The reason your original command doesn’t work is that you are both quoting and escaping the path name. If you are using backslashes for spaces in the path, then you would not put it in quotes.
E.g. use one or the other, but not both:
// Escaped form - spaces must be preceeded by backslashes
/Applications/Mail\ Archiver\ X\ 6.1.3.app/Contents/Resources/de.lproj/InfoPlist.strings
// Quoted form - spaces are not escaped
"/Applications/Mail Archiver X 6.1.3.app/Contents/Resources/de.lproj/InfoPlist.strings"
Also, I believe you can combine escaped and unescaped paths if you get the quoting right, e.g. /Path \ to \ my \ app\".app/some subfolder with spaces/" is a legit way to do it, combining the two styles.