Amazon plugin translation

Hi,

I am trying to translate some english phrases to German, because all the rest of the shop is in German. I use a custom template, actually a child of a custom template: Marketpress Hamburg.

I go to Loco, click on Amazon plugin which has no languages yet, add a new language, replace the phrace with what I would like to have and save it.

The site shows the english original. Great.
I have tried to add another english version and save it. No change.
I have tried to find the phrase somewhere, no luck.

Loco Translate does exactly nothing, asks for PO, MO, can SYNC (whatever that means) – I just want to select a language, edit my text and save. Why is it so complicated and after all: why is not working???

I am really annoyed, sorry. Any help is greatly appreciated.
Thank you.