Node editing language and interface language

Editing nodes in one language with a different interface language can be a bit confusing for some users. This is more problematic when you are viewing a node and click to add translation. You are forced to edit that translation on the original node language. The language switcher doesn't work and the only way to change the language is to manually edit the path prefix at the URL. For my site, I would prefer if the interface language switched automatically to match the translation language. I know this solution does not apply to everyone and I think I know why.

For sites that a lot of people are editing content and without any kind of knowledge of the platform (wikis), the best solution is to keep things simple and in this case is matching the languages. Why? Because this way the user knows, for sure, in which language he/she is working. There is no ambiguity here. And also, a user might not understand perfectly the language of the source translation and when chooses to add a translation for his/hers own language is expecting the interface language to change as well (you might be asking why a person who does not understand a language is translating a node from that language, but don't forget that translating nodes is different that translating content. The content might be different but refer to the same subject).

However, for sites with less people people as editors, their level of the understanding of the platform might be greater and therefore the matching of the content language and the interface language does not need to be implemented. So in this case a simplification is obtained by separating interface language and node language so that if users want to translate content but keeping their language they can. However, for this to work correctly one issue needs to be solved. When editing a node and changing the language flag, the information already implemented is lost; this has harmful consequences in node translations - if a translation is being edited and the language is switched the user is presented with a plain 'create node' page.

So, what I suggest for solving this issues is:
1 - create an option in the administration screens, that allows to lock the interface language to the node editing language if set. This can be enabled for only certain users roles.
2 - solve the language switcher issue, so that if admins want the other way around they can allow their editors to choose the interface language while editing content independently of the content language.