A few sentences in this lesson also do not accept "that" for "to/ta/ten". I assume these terms just haven't been added yet, correct?
yes, you should be able to translate "ta" to "that", but it is not added to all sentences, so try to use "this", and please report.
I always use that so I can report it if I find a missing "that." I just asked this time because I don't think "that" was accepted anywhere in this lesson, so I was thinking there might be a reason for it.
Well, it's not a translation of the Polish sentence, because "idę" happens right now, it takes Present Continuous.
Until now you had only verbs that can translate either into Present Simple or Present Continuous, but Verbs of Motion actually show this difference.