URL scheme for a multi-version web app

Question

I'm looking for the best URL schema to use for a web app that has multiple versions, namely several languages and a simplified version for use by mobile phones - both aspects can be combined, so there's an English regular and mobile version, a German regular and mobile version, etc.

Goals (in order of importance):

• User-friendliness
• Search engine friendliness
• Ease of development

Aspects to consider:

• How should the URLs look like?
• How should the user navigate between versions?
• How much logic should there be to automatically decide on a version?

I'll describe my concept so far below, maybe some of you have better ideas.

Answer 1

My current concept:

• When a new user arrives, the app decides, based on cookies (see below), the Accept-Language: header and the user agent string (used to identify mobile browsers) which version to show, but does not reflect this in the URL (no redirects)
• It defaults to the non-simplified English version
• There are prominently displayed icons (flags, a stylized mobile phone) to choose other versions
• When the user explicitly chooses a different version, this is reflected both in a changed URL and a browser cookie
• The URL schema is / for the "automatic" version, /en/, /de/, etc. for the language version, /mobile/ for the simplified version, /normal/ for the non-simplified one, and combinations thereof i.e. /mobile/en/ and /normal/de/
• mod_rewrite is used to strip these URL prefixes and convert them to GET parameters for the app to parse
• robots.txt disallows /mobile/ and /normal/

Advantages:

• The different language versions are all indexed separately by search engines
• Cookies help, but are not necessary
• There'S a good chance that people will see the version that's ideal for them without having to make any choice
• The user can always explicitly choose which version he wants (this makes the /normal/ URL necessary)
• Each version has an URL which will display exactly that version when passed to others
• /mobile/ and /normal/ are ignored by search engines; they would only be duplicate content.

Disadvantages:

• Requires heavy use of mod_rewrite, which I find rather cryptic
• Users could send their current URL to someone and that person, when visiting it, could end up seeing a different version, which could cause confusion
• There is still duplicate content between / and /en/ - I can't disallow / in robots.txt - should I trust the search engines not to penalize me for exact duplicate content on the same domain, or disallow /en/ and accept that people coming to / via a search engine may see a different version than what they found in the search engine?

Answer 2

I am unclear why you would want to incorporate any kind of what you call versioning information, such as accept-language or user-agent, specific designation in the URL scheme. The URL scheme should be indicative of the content only. The server should investigate the various request headers to determine how to retrieve and/or format the response.

Answer 3

I suggest subdomains, personally.

I wouldn't include the mobile at all - use the useragent to determine this, and possibly a cookie incase the user wants to view the full site on their mobile (think how Flickr and Google do it). But for languages, yes - primary language at http://mydomain.com/, secondary languages at i.e. http://de.mydomain.com/ or http://fr.mydomain.com/