Ios – Base localization + Storyboard + .strings -> no localization

Xcode 4.6, target iOS 6, SDK iOS 6.1

I started with a storyboard that worked well for my app; the strings it contains are in English. I wanted to add a French localization. I did this:

• Added a base localization, which transferred
  MainStoryboard.storyboard from en.lproj to Base.lproj.
• Added a French localization, which cloned InfoPlist.strings (English)
  and MainStoryboard.storyboard (Base) into fr.lproj.
• Changed a couple of strings (titles of segments in a
  UISegmentedControl) in the French MainStoryboard.storyboard.
• In the Simulator, set the language to French.
• Ran the app from Xcode.

Result: This worked; my changed strings showed up in the running application.

But I want to be all fancy. I want to do the French localization using a .strings file. (It's not just a matter of being fancy; the French localization will be turned over to nontechnical translators, who can't be expected to master Interface Builder.) So:

• Selected the base MainStoryboard.storyboard in the Xcode Project
  navigator.
• In the File inspector, under Localization, changed the French
  localization from "Interface Builder Cocoa Touch Storyboard" to
  "Localizable Strings."
• Accepted Xcode's warning that the French storyboard will be discarded
  in favor of a .strings file, which appears in the Assistant editor.
• Made the same two edits; there's no question of their being the wrong
  strings, because they're all commented as
  IBUISegmentedControl…segmentTitles; and the label text doesn't
  appear anywhere else in the .strings file.
• Deleted the existing (working) copy of the app from the simulator.
• Ran the app.

Result: The view uses the base (originally English) localization, instead of loading the French strings.

Converting to Autolayout had no effect. Deleting the app from the simulator had no effect. Deleting the Derived Products directory had no effect. A Stack Overflow suggested using ibtool to generate the .strings file instead of Xcode; the two generated files are identical.

This isn't satisfactory. As I said, I can't turn a .storyboard file over to a nontechnical translator. How can I get iOS to accept the storyboard localizations from a .strings file?