I observed that machine translation in Google Translate Toolkit used English as an intermediate stage for translating German to Vietnamese.
In this screenshot, the use of English is obvious that caused failure in Vietnamese translation:
- Example 1:
German: A Kolbenfläche (in which letter A represents a notation that appears in a picture)
English (machine translation): A piston surface
Vietnamese (machine translation): Một bề mặt piston
(how can “A” in German be translated as “một” in Vietnamese?!)
- Example 2:
German: s Kolbenhub (in which letter s represents a notation that appears in a picture)
English (machine translation): s piston stroke
Vietnamese (machine translation): đột quỵ của piston
(here, via English, “stroke” is translated as “đột quỵ” in Vietnamese by the machine!)
Another word in the screenshot: “Hubzahl” (German) is also translated as “stroke” (English) then “đột quỵ” (Vietnamese). The correct translation should be “hành trình”, as pointed out in the dictionary http://www.tudien.vsw-ubtt.com/ (see the right part of the screenshot).

Info on Google’s translate engine:
https://en.m.wikipedia.org/wiki/Google_Neural_Machine_Translation