Thank you, xulihang. You have helped me a lot. Here is my quick solution ...
Sub Process_Globals
Private fx As JFX
Private MainForm As Form
Private xui As XUI
Private Button1 As B4XView
Private Job As HttpJob
End Sub
Sub AppStart (Form1 As Form, Args() As String)
MainForm = Form1
MainForm.RootPane.LoadLayout("Layout1")
MainForm.Show
End Sub
Sub Button1_Click
Job.Initialize("Translate", Me)
Job.poststring("
https://api.mymemory.translated.net/get","q=Heute ist ein schöner Tag!&langpair=de|en")
End Sub
Sub JobDone (Jobe As HttpJob)
Dim x,y As Int
x = Job.GetString.IndexOf("translatedText") + 18
y = Job.GetString.IndexOf("match")-38
Log(Mid(Job.GetString(),x,y))
End Sub
Sub Mid(Text As String, Start As Int, Length As Int) As String
Return Text.SubString2(Start-1,Start+Length-1)
End Sub