What is the procedure if the "sourceLocale" is not English?

[ChristophM2000]

If my "sourceLocale" is "en", then everything fits together. Kendo's "sourceLocale" is "en" and if I want to translate my application into German, for example, I create a "messages.de.xlf" file with "ng extract-i18n" into which I then merge the Kendo translations with "npx kendo-translate messages.de.xlf --locale de".

But what if my source locale is "de"? Then there is no file "messages.de.xlf" for the language German into which "kendo-translate" could put its translations.
The end result is that I have an application in which on the one hand my own texts are in German and the texts from Kendo are in English.

How can this scenario be solved?