SwiftUI string interpolation and localisation

Hello,

I was watching the WWDC video:

Introducing SwiftUI: Building Your First App

https://developer.apple.com/videos/play/wwdc2019/204/

The had some sample code at 48:32 for localising the string used in in

Text("\(room.capacity) people")

They used a stringdict file, but didn't expand on the details of configuring the string (here's the file I created in plain xml):

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>%lld people</key>
  <dict>
  <key>NSStringLocalizedFormatKey</key>
  <string>%#@VARIABLE@</string>
  <key>VARIABLE</key>
  <dict>
  <key>NSStringFormatSpecTypeKey</key>
  <string>NSStringPluralRuleType</string>
  <key>NSStringFormatValueTypeKey</key>
  <string></string>
  <key>zero</key>
  <string></string>
  <key>one</key>
  <string></string>
  <key>two</key>
  <string></string>
  <key>few</key>
  <string></string>
  <key>many</key>
  <string></string>
  <key>other</key>
  <string></string>
  </dict>
  </dict>
</dict>

The only thing they showed in the conference video was

<key>%lld people</key>

What should I do to complete the details for this string (in the Localizable.stringdict file) to be picked up by SwiftUI automatically and be localised (e.g. in french?), I did the other strings (the plain - not interpolated ones) in a Localizable.strings file and they localised fine.

Also, is that %lld people (as two Ls or two capital i's in the %LLD or %IID?)

Thanks