What are the considerations in setting language within the url of multilingual sites?

[CanadaPost]

Is it good practice to use Language-Agnostic + LOCALE=en +LOCALE=fr (as per example below)? If not what is the best way to determine language within a url and why?

For example, today we use:

http://www.canadapost.ca/cpo/mc/default.jsf (goes to language last used by user)

http://www.canadapost.ca/cpo/mc/default.jsf?LOCALE=fr (forces a French-launguage page)

http://www.canadapost.ca/cpo/mc/default.jsf?LOCALE=en (forces and English-language page)

I think you can get tell Google about these parameters through Webmaster tools to help them properly crawl and understand your content, but if we had the opportunity to change it what should we do?

[Aeronet]

I think subfolders accompanied with geotargeting in GWT would work nicely in your case. (canadapost.ca/en/ and canadapost.ca/fr/) but it demands some preparations (301 redirect for example) and it will not be easy technically to change that in your website.