Variable variables in Twig
In order to pull this off, you'll need to take advantage of the not very well  documented _context variable in Twig.  This should do it:

{% set language = 'fr' %}

{% set foobar = _context[language ~ "_foobar"] is defined ? _context[language ~ "_foobar"] : null %}

{% if foobar %}
    {{ foobar.globalAddress }}
{% endif %}