Hi Andoni,
Thanks al ot for the detailed information, it all sounds more than good!
Regarding your concern, it isn't necessary having an English certificate for this position, but it is required a certain level, at least being able to communicate.
We would very much like to move forward in the process by arranging a call with you. How about Thursday at 12:30h CET? I will send you a google calendar invite, it will be a Google Meet call (you'll find the link within the invitation). If the proposed time is not suitable for you, just let me know :)