In fact, what we really need is to extend the L10n capabilities to be able to check if certain string conforms to any of the locale strings, for example:
l10n.isValid('12:34', 'callDurationMinutes'); // True if the language is English, for example.
l10n.isValid('12&34', 'callDurationMinutes'); // False if the language is English, for example.
But definitely something to deal with in another bug :-)
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