Then you're probably out of date. Please update and retest. There were some offset problems which are now fixed. It was doing offset from GMT instead of using timezones. When doing offset it can't figure out that in 2011 for example it might have been DST, but with timezones it can. We now use timezones for the JS usage like we do for the PHP usage. Latest release does not offset Date fields at all (in JS or PHP) so your issue is literally an impossibility unless something else is modifying the data.

Then I'm out of ideas as to what is causing your issue. I'm not able to confirm your issue regardless of timezone settings as again the Date field entirely ignores them now. Even using your exact settings I am unable to confirm. You couldn't have been using latest release if you're still seeing that offset parameter for a Date field. Are you sure you're not using a Datetime field? They are two different fieldtypes.

Edit: Noticed you're on PHP 7. Maybe that's the cause? Are you able to downgrade to PHP 5.6 and see if issue persists?

Language shouldn't have anything to do with the timezone offset of fields. That parameter is flat out removed for Date fields in latest CB build. It doesn't exist anymore. If you're still seeing it you're either out of date or you are using a Datetime field.