Remove needless leading dash on Main Page interlanguage links

Adds a message "interlanguage-link-title-langonly" with contents "$1",
to allow customization of the tooltip in all circumstances.

Bug: 55865
Change-Id: Icd348919377bac77e27018a44e981028a263c6e1
Merge "Remove needless leading dash on Main Page interlanguage links"