Fixed getting names of languages

When one of the already translated languages ​​in the context was removed from the available languages ​​In Plone Site, KeyError as this was raised

```
2012-05-03 17:07:04 ERROR Zope.SiteErrorLog 1336054024.750.875950689959 http://localhost:8080/lingua/danish-welcome/manage_translations_form
Traceback (innermost last):
  Module ZPublisher.Publish, line 126, in publish
  Module ZPublisher.mapply, line 77, in mapply
  Module ZPublisher.Publish, line 46, in call_object
  Module Shared.DC.Scripts.Bindings, line 322, in __call__
  Module Shared.DC.Scripts.Bindings, line 359, in _bindAndExec
  Module Products.CMFCore.FSPageTemplate, line 237, in _exec
  Module Products.CMFCore.FSPageTemplate, line 177, in pt_render
  Module Products.PageTemplates.PageTemplate, line 79, in pt_render
  Module zope.pagetemplate.pagetemplate, line 113, in pt_render
  Module zope.tal.talinterpreter, line 271, in __call__
  Module zope.tal.talinterpreter, line 343, in interpret
  Module zope.tal.talinterpreter, line 888, in do_useMacro
  Module zope.tal.talinterpreter, line 343, in interpret
  Module zope.tal.talinterpreter, line 533, in do_optTag_tal
  Module zope.tal.talinterpreter, line 518, in do_optTag
  Module zope.tal.talinterpreter, line 513, in no_tag
  Module zope.tal.talinterpreter, line 343, in interpret
  Module zope.tal.talinterpreter, line 954, in do_defineSlot
  Module zope.tal.talinterpreter, line 343, in interpret
  Module zope.tal.talinterpreter, line 533, in do_optTag_tal
  Module zope.tal.talinterpreter, line 518, in do_optTag
  Module zope.tal.talinterpreter, line 513, in no_tag
  Module zope.tal.talinterpreter, line 343, in interpret
  Module zope.tal.talinterpreter, line 858, in do_defineMacro
  Module zope.tal.talinterpreter, line 343, in interpret
  Module zope.tal.talinterpreter, line 954, in do_defineSlot
  Module zope.tal.talinterpreter, line 343, in interpret
  Module zope.tal.talinterpreter, line 533, in do_optTag_tal
  Module zope.tal.talinterpreter, line 518, in do_optTag
  Module zope.tal.talinterpreter, line 513, in no_tag
  Module zope.tal.talinterpreter, line 343, in interpret
  Module zope.tal.talinterpreter, line 946, in do_defineSlot
  Module zope.tal.talinterpreter, line 343, in interpret
  Module zope.tal.talinterpreter, line 583, in do_setLocal_tal
  Module zope.tales.tales, line 696, in evaluate
   - URL: file:/data/kroman0/bdcache/eggs/Products.LinguaPlone-4.1.2-py2.6.egg/Products/LinguaPlone/skins/LinguaPlone/manage_translations_form.pt
   - Line 8, Column 0
   - Expression: <PathExpr standard:u'here/getDeletableLanguages'>
   - Names:
      {'container': <PloneSite at /lingua>,
       'context': <ATDocument at /lingua/danish-welcome>,
       'default': <object object at 0xb76de7c0>,
       'here': <ATDocument at /lingua/danish-welcome>,
       'loop': {},
       'nothing': None,
       'options': {'args': ()},
       'repeat': <Products.PageTemplates.Expressions.SafeMapping object at 0xb4a328ec>,
       'request': <HTTPRequest, URL=http://localhost:8080/lingua/danish-welcome/manage_translations_form>,
       'root': <Application at >,
       'template': <FSPageTemplate at /lingua/manage_translations_form used for /lingua/danish-welcome>,
       'traverse_subpath': [],
       'user': <PropertiedUser 'admin'>}
  Module zope.tales.expressions, line 217, in __call__
  Module Products.PageTemplates.Expressions, line 155, in _eval
  Module Products.PageTemplates.Expressions, line 105, in render
  Module Products.PageTemplates.ZRPythonExpr, line 80, in call_with_ns
  Module Products.CMFCore.FSPythonScript, line 122, in __render_with_namespace__
  Module Shared.DC.Scripts.Bindings, line 336, in __render_with_namespace__
  Module Shared.DC.Scripts.Bindings, line 359, in _bindAndExec
  Module Products.PythonScripts.PythonScript, line 344, in _exec
  Module script, line 1, in getDeletableLanguages
   - <FSPythonScript at /lingua/getDeletableLanguages used for /lingua/danish-welcome>
   - Line 1
  Module Products.LinguaPlone.browser.translate, line 82, in getDeletableLanguages
KeyError: 'fr'
```