translations missing for QPlatformTheme dialog button labels

On 5.3 branch, git grep will find the following ts files that have QPlatformTheme:

translations/qtbase_cs.ts: <name>QPlatformTheme</name>
translations/qtbase_de.ts: <name>QPlatformTheme</name>
translations/qtbase_fi.ts: <name>QPlatformTheme</name>
translations/qtbase_it.ts: <name>QPlatformTheme</name>
translations/qtbase_ja.ts: <name>QPlatformTheme</name>
translations/qtbase_ru.ts: <name>QPlatformTheme</name>
translations/qtbase_uk.ts: <name>QPlatformTheme</name>

but on stable branch they have gone missing. The result is that dialog buttons are not getting translated. The call to translate is in

QString QPlatformTheme::defaultStandardButtonText(int button)

    switch (button) {
    case QPlatformDialogHelper::Ok:
        return QCoreApplication::translate("QPlatformTheme", "OK");
...