manual: Translation links from wiki broken in FreedomBox's online help

In version 20.12.1 the links in a non-english configured FreedomBox's online help double the language code.

For example, in a spanish configured FreedomBox the link https://wiki.debian.org/es/es/FreedomBox/Features# has a double es (es/es) that breaks the URL. It should have been generated as https://wiki.debian.org/es/FreedomBox/Features#.