> but before going into interface questions, what are the items related
> to language?

  The question of what to use as first and second order quotation marks
seems to be language related:
  In US English (and Swedish), quotes are nested as
    ``And then he said `foo bar', ... ''
whereas in UK English, it is
    `And then he said ``how bad'', ... '
I think.

* In US English, the number 1e9 is typeset as "one billion", whereas in UK
English, it is typeset as "one milliard". (After the French revolution, the
metric system, and the system with "milliard" was invented, and the
British, as the Swedes, started using that; later the French switched back
to the original system, the used in the US.)
  In principle, one could think of special commands for cardinal numbers;
one might the use the source code, to see which number was intended. :-)

  Hans Aberg