Which time should be followed for prayer times, Imsak, and Iftar in Ramadan, if the Adhan times vary from one mosque to another in Germany?

If you are unable to determine prayer times by the শরعي (Shari'ah-compliant) signs, and the calendars diverge, then act according to the calendar approved by trustworthy scholars. If such a calendar is not available, or if more than one trustworthy calendar exists, then act according to the latest entry of prayer times. Therefore, do not pray or break your fast until after the latest time given by the two calendars. As for abstaining from food and drink during fasting (Imsak), you may eat and drink until the prayer time enters according to the later calendar. However, it is more cautious to observe Imsak according to the earlier calendar.