Ability to query addresses in multiple languages simultaneously
Streets and cities may have names in multiple languages, and we don't always know in advance which language the user is going to query the parts of the address in. If we return with default language, the user sees the result in one language, but the street address may have been in different language than the city name in the query. In order to check that street and city was indeed the ones given by the user, it would be helpful to get results in multiple languages instead of one.
In practice, this would mean 1) allowing a list of languages in the parameters (&language=fr-FR,de-DE) or 2) adding all matching names from different languages to the results - the street name and municipality fields do already allow returning multiple values.
There are no plans to add such a feature at this time. Leaving this open for now so that others may vote up if they feel it is needed and we can revisit then.
The input can be in any supported language and the geocoder will do its best to try and understand it and find a valid match. If a language is specified in the request it will try and return a result in that language, however this doesn't always happen as street names are no localized globally and often don't make sense to translate.