This might be totally wrong but earlier you mapped languages in episerverframework.config. Might be in adminmode from 7.5. It might also be a bug as you mentioned if your setup is correct. :)
Thank you for the response, Eric.
I'll contact the support for further clarifications.
I got this answer from support
The current functionality will show the link in the same language as the calling page branch.
A workaround can be to create an external URL, copy the public URL of the item you want to link to and then add "?epslanguage=[language key]".
EPiServer Developer Support
In a multi-language site I would like to link from a page in Spanish, for example, to an page in English.
This seems not to be possible. Even in "External URL" the link is rewritten to /es/.
Is this a bug, and if Yes, is there any workarounds for the editor?