If an incorrect system property for locale providers is set, it should be logged and presetned to the user, but it's not in reality. There's such code in LocaleProvderAdapter static initializer:
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                } catch (IllegalArgumentException | UnsupportedOperationException e) {
                    // could be caused by the user specifying wrong
                    // provider name or format in the system property
                    LocaleServiceProviderPool.config(LocaleProviderAdapter.class, e.toString());
                }
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However, this ends up in jdk.internal.logger.SurrogateLogger which only logs JUL_DEFAULT_LEVEL( = PlatformLogger.Level.INFO) or more severe ones, ie., the message, which is CONFIG, will never be logged.