Basically, with a *french* account, you'll buy from Amazon *US*, and you'll have access to only a subset of content (due to a number of crappy reasons 'solved' by geo-lock).
Note that there is near zero 'new' content in non-English languages on Amazon.
As others said, you will be able to buy content eslewhere, provided it's DRM-free, available from your location, and converted to MOBI if need be.
EDIT: In short, like Eowyn said, if you read in english, it's probably the best solution right now (while far from prefect if you don't want/can't/care to mess around a bit), if you don't, it's really, really not the right choice
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