Fiezangoz68 The language in the Dashboard you can change as shown in the picture below (yellow highlighted), then almost everything in MySwisscom will be shown in English, the language remains as long as you don't change it, even if you leave and re-enter MySwisscom.
The pdfs in the bills section and other documents are written in the correspondence language, see below:
Concerning the documents:
The correspondence language is in your case obviously set as German, this can be changed in the best way by calling the Hotline 0800 800800 (within MySwisscom the correspondence language can't be changed), then the pdfs will bein English (but I don't think this will be done retroactively).