I18n without translation

Question

Having a locale-aware application starting up for a locale without translation, which behavior is best from the user experience point:

• Fall back to a supported locale (and give the user the option to select another locale as well).
• Fall back to a supported translation, and keep numbers, currencies, etc. in the user's default locale.

In other words: should the format of numbers, currencies, etc. follow the user's locale even if there is no translation available?

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Example: Consider an application, in en-US, displaying "1,000.00 units". The application is now started on a device whose default locale is de-DE.

The correct translation would be "1.000,00 Einheiten" - but assume the application has not been translated into German, so "Einheiten" is unknown. Should the application now rather display "1,000.00 units" or "1.000,00 units"?

Answer 1

I think there is no right or wrong answer to this question - It depends on the context. If it is very important and a main task to show the correct locale format, go with it - If not, think about the fact that implementing the unit locales but not string locales will result in something like (de-de) "Created – Gestern", or, "Created – 18.12.2015" which can not only lessen trust in the product but also confuse user as to why there is a mix between languages or formats.