Payment SuccessUrl/RouteUrl/cancel_url in the wrong language

Does someone know why Nop includes wrong the language in the URL i?

I have configured 2 languages and SEO friendly URLs. (restarted and cleared the cache may times)
When I do the shopping in the German language the URL is like https://host.domain.ch/de/..
When I return from the checkout it redirects to the English "en" SEO URL and the languages switched to English.
https://host.domain.ch/en/

I saw that "en" is included in request regarding the payment provider.
SuccessUrl=https://host.domain.ch/en/plugins/...........
RouteUrl=/en/plugins/.........
https://host.domain.ch/en/plugins/......

Does someone has any ideas?
Manx thanks.

This issue  is my plugin only for Linux.
_workContext.WorkingLanguage.UniqueSeoCode
has this value "de"
but
urlHelper.RouteUrl(nameof(Product), new { SeName = "test"})
has this value "en/test".

Windows doesn't have such issue.

I have solved this issue.
I created URLs from the POST request without language suffix.  
I need to use this commad
urlHelper.RouteUrl(nameof(Product), new { SeName = "test", language = _workContext.WorkingLanguage.UniqueSeoCode})

Close this ticket.

Thank you so much for your fast response time and great support. It's really a please to work with you!

It is working correctly in both languages.    :-)