Translation:My grandmother did not understand this German.
Yes. This German man.
"this German woman" would be "tej Niemki" (Nominative: ta Niemka).
I put : "She was not understanding this german"
And it said it is wrong because it should be: "She did not understand this german"
Can then someone please enlighten me how you would say "she was not understanding this german" ?
The use of the progressive construction with "understand" sounds a bit odd - one has to construct quite a specific context to make it sound okay. The simple past is more neutral.