general: gettextize three overlooked statusbar messages

This fixes https://savannah.gnu.org/bugs/?48622.

src/browser.c

@@ -69,7 +69,7 @@ char *do_browser(char *path)
 	dir = opendir(path);
 
     if (path == NULL || dir == NULL) {
-	statusline(ALERT, "Cannot open directory: %s", strerror(errno));
+	statusline(ALERT, _("Cannot open directory: %s"), strerror(errno));
 	/* If we don't have a file list yet, there is nothing to show. */
 	if (filelist == NULL) {
 	    napms(1200);
@@ -375,7 +375,7 @@ char *do_browse_from(const char *inpath)
 
 	    if (path == NULL) {
 		free(currentdir);
-		statusline(MILD, "The working directory has disappeared");
+		statusline(MILD, _("The working directory has disappeared"));
 		beep();
 		napms(1200);
 		return NULL;

src/files.c

@@ -912,7 +912,7 @@ void read_file(FILE *f, int fd, const char *filename, bool undoable, bool checkw
     openfile->placewewant = xplustabs();
 
     if (!writable)
-	statusline(ALERT, "File '%s' is unwritable", filename);
+	statusline(ALERT, _("File '%s' is unwritable"), filename);
 #ifndef NANO_TINY
     else if (format == 3) {
 	/* TRANSLATORS: Keep the next four messages at most 78 characters. */