If these were the possible URL's tied to a Virtual Server:
http://www.website.com/english
http://www.website.com/french
http://www.website.com/german
These would be the values of the [HTTP::host] and [HTTP::uri] values:
[HTTP::host] = www.website.com
[HTTP::uri] = /english, /french, or /german
string tolower [HTTP::uri] takes the value of the [HTTP::uri] and forces all upper case characters to lower case (basically putting them into a "known" format for comparison). Example:
/ENGLISH would be converted to /english
/English would be converted to /english
switch -glob is a string compare of the specified value.
Example. If the incoming URL was this:
http://www.website.com/ENGLISH
The /ENGLISH would be forced to lower case (/english) and then compared for a match to the provided vaules:
"/english*" { pool pool.for.english }
"/french*" { pool pool.for.french }
"/german*" { pool pool.for.german }
If a match is found then it will take whatever action is specified in the { } for that match. In this case it will send the traffic to a pool of server named "pool.for.english".
Hope this helps.