Web Forms :: Non - Standard Letters In QueryString

In short, I want to implement a search engine. I pass the search string as a http querystring and my database uses it as a filter in Select. The problem occurs when I enter some non-standard english letters. Let me elaborate: on Main.aspx page, when I click on "Search", a function calls "Main.apsx?search=something". The querystring is passed as a filter to the database which returns values depending on the filter. The database holds correct data at the moment.

After that, I dynamically modify some hyperlinks' url to something like this: hlink[i].NavigateUrl = "Detail.aspx?search=" + base.Request.QueryString["search"] + some integers;. I want users to be able to click on the link to get details on the result. If they click the link, since a new page is now opened, the database has to be refilled (from cache). The same function for filtering the main database is called with a querystring which should be the same as the search string, but somehow it isn't. It looks like something was lost in a conversion or something. If I use standard english letters, everything works fine. I noticed that prior clicking the link the query string had a value like /u0100d for the non-standard letter, but after clicking the link the value had changed to something like /u0ffff. It obviously isn't the same when typing something in the search box and hitting "search", and when putting this search string into NavigateUrl and clicking on it.