iRule to detect browser language and re-direct

You'd probably also want to only check a few URIs (/ and the main index page come to mind) so you're not checking the header on every request. Also, if the help pages are on the same VS as this iRule, you'd need some kind of logic to avoid a loop of redirects.

You can use Fiddler (or an iRule even) to manipulate the Accept-Language header value: HTTP::header replace Accept-Language "my-new-language"

To add to Colin's point, the Accept-Language header can have a preferential list:

http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html

14.4 Accept-Language

The Accept-Language request-header field is similar to Accept, but restricts the set of natural languages that are preferred as a response to the request. Language tags are defined in section 3.10.

Accept-Language = "Accept-Language" ":"

1( language-range [ ";" "q" "=" qvalue ] )

language-range = ( ( 1*8ALPHA *( "-" 1*8ALPHA ) ) | "*" )

Each language-range MAY be given an associated quality value which represents an estimate of the user's preference for the languages specified by that range. The quality value defaults to "q=1". For example,

Accept-Language: da, en-gb;q=0.8, en;q=0.7

would mean: "I prefer Danish, but will accept British English and other types of English." A language-range matches a language-tag if it exactly equals the tag, or if it exactly equals a prefix of the tag such that the first tag character following the prefix is "-". The special range "*", if present in the Accept-Language field, matches every tag not matched by any other range present in the Accept-Language field.

Note: This use of a prefix matching rule does not imply that

language tags are assigned to languages in such a way that it is

always true that if a user understands a language with a certain

tag, then this user will also understand all languages with tags

for which this tag is a prefix. The prefix rule simply allows the

use of prefix tags if this is the case.

The language quality factor assigned to a language-tag by the Accept-Language field is the quality value of the longest language- range in the field that matches the language-tag. If no language- range in the field matches the tag, the language quality factor assigned is 0. If no Accept-Language header is present in the request, the server

SHOULD assume that all languages are equally acceptable. If an Accept-Language header is present, then all languages which are assigned a quality factor greater than 0 are acceptable.

It might be contrary to the privacy expectations of the user to send an Accept-Language header with the complete linguistic preferences of the user in every request. For a discussion of this issue, see section 15.1.4.

As intelligibility is highly dependent on the individual user, it is recommended that client applications make the choice of linguistic preference available to the user. If the choice is not made available, then the Accept-Language header field MUST NOT be given in the request.

Note: When making the choice of linguistic preference available to

the user, we remind implementors of the fact that users are not

familiar with the details of language matching as described above,

and should provide appropriate guidance. As an example, users

might assume that on selecting "en-gb", they will be served any

kind of English document if British English is not available. A

user agent might suggest in such a case to add "en" to get the

best matching behavior.

Here's a blog showing a method for parsing the header:

http://www.thefutureoftheweb.com/blog/use-accept-language-header

I think you could probably cheat a bit and just look at the first language up to the first comma and switch on that:

switch -glob [getfield [HTTP::header Accept-Language] "," 1]

Of you could read these into a TCL list and evaluate them one by one until you find a match:

foreach line [split [HTTP::header Accept-Language] "," ] {
   switch -glob [getfield $line ";" 1] {
      "de*" {

         ...

          Break out of the loop as we found a match
         break
   }
}

I could see this looping being expensive though.

Aaron