Is there a way to check whether unicode text is in a certain language?

You can use regular expression to match with Supported Named Blocks:

private static readonly Regex cjkCharRegex = new Regex(@"\p{IsCJKUnifiedIdeographs}");
public static bool IsChinese(this char c)
{
    return cjkCharRegex.IsMatch(c.ToString());
}

Then, you can use:

if (sometext.Any(z=>z.IsChinese()))
     DoSomething();