localize sublinks so you stay on the current language

• go to https://lektor-staging.torproject.org/tpo/staging/es/about/history/
• click on 'informes' on the menu under the title
• you are sent to /staging/about/reports/ , instead of /es/staging/about/reports/ (mind the /es).

what should happen:

• You stay navigating in /es/ as you have selected it previously.

note: it works ok for button About that is part of the menu at the top of the page: that button changes along with the selected language.