Without seeing the difference and just based on encoding, you can determine if it's japanese by checking the unicode value of the text.
VB Code:
Private byt() As Byte = {56, 0, 57, 0, 67, 0, 13, 0, 74, 81, 75, 81, 76, 81}
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Me.RichTextBox1.Text = System.Text.Encoding.Unicode.GetChars(byt)
For Each chr As Char In Me.RichTextBox1.Text
JapaneseEnglish(chr)
Next chr
End Sub
Private Sub JapaneseEnglish(ByVal chr As Char)
If System.Text.Encoding.Unicode.GetBytes(chr)(1) = 0 Then
MessageBox.Show("English")
Else
MessageBox.Show("Japanese")
End If
End Sub
This is a very crude way of determining the language, but it will work... You'll also have to take into account that numbers fall on either side of the fence. There's probably more exceptions, but this is one way.
(Forgive me... The characters are chinese, but I'm not familiar with the language)