Tested in Odoo 11 and 12, when I want to edit a page translation I have first to click on the target language in the language switcher (by default at the bottom). When I do so, I can see the "translate" button and edit translation but all the UI has been changed to the targeted language too. Is there any way to retain the current user language for the "odoo admin ui" part and only let people change translatable strings.