Hi Naru,
Your English is better than my German. (Or any European language for that matter—despite that I studied several at one time or another. Sad!)
I’m so sorry you and your yorkie are dealing with this.
I'm not a nurse or vet, and have really only dealt with sporadic mushy poo-poo in a senior yorkie. Maybe if we exchange additional information, those who have more experience with chronic, albeit seems sporadic, diarrhea will comment.
Diarreha is a scary, particularly so for these little ones. There can be one or more contributing factors.
WebMD/Pets lists no fewer than 15 different causes. See: “
Diarrhea in Dogs:Causes and Treatment.“
While diarrhea causes health problems, it can be a symptom of underlying illness, too.
What does the diarrhea look like? What color is it? Does it always look like that; is it always that color?
See also article on
YorkieInfoCenter, “
Yorkie Diarrhea” (n.d., no attribution),