If you come across a website in a mystery language, try Linguid. Maciej Cegłowski's site is a “statistical language identifier” which requires “at least 20 characters of UTF-8 encoded text” in order to attempt to guess the language. It picks up Welsh, no problem at all.
Telling your Gibberish from your Swahili
Previous post: The last day of virtual Etech
Next post: Eastward ho!

Serendipity! Some guy just linked to me and I had no idea what language it was. You just saved me from writing this tool myself.
We met briefly at Northern Voice — been reading your blog ever since.
– Neil K.
It picked up this dutch phrase as Norwegian :p
“hallo ik wil u eraan herinneren”
Bram
Well, it is guessing!
Hi Neil! Glad to have been of service, and glad that you're enjoying the blog! (Well, glad anyone is, really!)