<bing:TileLayer ID="BingLayer" LayerStyle="Road" Visible="True" ServerType="Production" Culture="fr-FR" Token="{StaticResource BingKeyString}" />
I don't think that arcgisonline supports localized tiled services.
But with Bing maps, you can change the labels by using the Culture property of the TileLayer.
l
Concerning the geocoding, you have to use the appropriate geocoder which is managing the addresses for the region.
For example, this geodocer gives results for french addresses:
http://tasks.arcgisonline.com/ArcGIS/rest/services/Locators/TA_Address_EU/GeocodeServer/findAddressC...
l