App localization is important, but tedious to test. One quick way is test localizations in the simulator, using launch arguments. In Xcode, click on Edit Scheme > Run > Arguments and add the following to Arguments Passed On Launch:

-AppleLanguages (en)

Replace en with the localization (zh, es, etc) you want to test e.g.

Simplified Chinese:
    -AppleLanguages (zh)

German:
    -AppleLanguages (de)

French:
    -AppleLanguages (fr)

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